[#highdef]: High-definition

This phrase has commonly been used to refer to graphics. Specifically, this referred to having more graphical detail (by having more pixels) than lower resolution. Even more specifically, manufacturers of video equipment like televisions (and, as additional examples, video game systems, movie playback equipment) have been known to use the term to refer to equipment that supports certain resolutions. This topic is discussed more in the section on HDTV.

There may also be other uses of HD referring to “high-definition”. Perhaps see: Wikipedia's disambiguation page for “High-definition”.

[#hdhrddrv]: Hard drive

A hard drive has also been known less commonly as a hard disk drive. However, the nice thing about the phrase “hard disk drive” is that its abbreviation, HDD, is less commonly used for other meanings. Therefore, HDD is probably a preferred abbreviation. Similar abbreviations may include: FDD (floppy disk drive), ODD (optical disc drive, referring to CDs (compact discs) or DVDs or BDs (Blu-Ray discs), or SSDs (solid-state disk/drive).

Although SDDs were categorized as being notably different than a hard drive, mostly noting that hard drives use magnetic platters and more moving parts, many people have become used to referring to a computer's primary storage as a “hard drive”. Therefore, when seeing a reference to an HDD (or even the words “hard drive”), many (especially older) pieces of documentation may be meaning to refer to the generalized concept of non-violatile primary storage devices that can hold a rather substantial amount of space (which meant megabytes in previous years, and has grown to gigabytes, and has grown further to at least terabytes). So, do not always just automatically assume that a reference to a “hard drive” was intended to exclude newer technologies like an SDD.

[#hddabbr]: HDD

hard disk drive. (See further discussion in the section for HD: hard drive.)

[#hdtv]: High-definition television

Sometimes this is just referred to as “HD”, which is simply an abbreviation for “high-definition.

Equipment that supports vertical resolutions containing at least 1,080 rows of pixels, instead of older standard resolutions of 625 rows or less (Wikipedia's article on 528i refers to 625 lines). 720 rows has been classified as “high definition” (e.g. Wikipedia's article for high-definition television mentions 720p), and has also been categorized as being one of the lower “standard” definitions (e.g. Wikipedia's page on Standard def TV refers to 720 in multiple places). The precise definition is not clearly defined (Wikipedia's article for “high-definition video” states, “ there is no standardized meaning for high-definition”). Wikipedia's article for “high-definition video”: “common high-definitino video modes” lists 1280x720, 1920x1080, and 2560x1440. Higher resolutions (2048x1536 and higher) are categorized (in the next chart on that same Wikipedia page) as “Ultra high-definition”.

More common standards were the 576 lines @ 50Hz (PAL/SECAM) standard used in many nations, or the 480 lines @ 60Hz (NTSC) standard used in some other nations (including all land on the North American continent). Compared to those lower resolutions, 1,080 rows was a more significant improvement.

[#hertz]: Hertz

A “cycle per second”.

In 1930, the International Electrotechnical Commission (“Commission électrotechnique internationale” in French) used the term Hertz when deciding on a term for the System International series of standard units. This is noted by Wikipedia's article for Heinrich Hertz, which goes on to note that the term “Hertz” “was adopted by the CGPM (Conférence générale des poids et mesures) in 1960, officially replacing the previous name, the "cycle per second" (cps).” The term is often abbreviated as Hz.

The term “Hertz” is named after Heinrich Rudolf Hertz, who studied electromagnetic waves. The term Hertz is used for various measurements of cycles per second, including electromagnetic radiation and sound.

Computer chips repeatedly go through cycles of being ready to perform a computer instruction, and then being busy applying one or more instructions. For many years, a key method of increasing overall computing speed was to increase how quickly the chips would be ready to process a new instruction. (Other methods of speed increase can relate to how effective the equipment operates each time it is ready to accept a new instruction. Having more cycles of being ready for a new instruction is one way to increase speed. Performing more math during each individual cycle is another method of increasing speed.)

Outside of the realms of computers and electronics, many people are familiar with the word “Hertz” as being the name of a company: Wikipedia's article for “The Hertz Corporation” notes, “Hertz is the largest U.S. car rental company” (based on sales), which now owns “Thrifty Car Rental” and “Dollar Rent A Car” (which used to compete, and which may still have stores operating under those names).


As an English word, this means a “curse”. However, in the world of computers, this is typically an abbreviation for “hexadecimal”.

In Greek, the prefixes “hex” and “hexa” meant six.

[#hexadec]: hexadecimal

Base 16. See how to count, converting between binary and hexadecimal

[#honeypot]: honeypot

A machine which is designed to attract attackers, possibly by being quite easy to attack. If all goes well, this may distract attackers so that they are less likely to attack a more valuable machine. The actions taken by attackers may be recorded, and that could help with defenses.

On the minus side, perhaps an attacker may be smarter than the person who set up and/or maintains the honeypot. An easily compromised machine may be, well, easily compromised. Then, perhaps the honeypot may be utilized by the attacker in a more successful way than expected.

There is some legal question regarding activity involving a honeypot. An arguement could be made that a honeypot is inviting connectivity, and that may reduce the effectiveness of a prosecutor's argument that an attacker was acting in an unauthorized manner. The process of capturing data via a honeypot may fit the legal definition of “entrapment”. Whether these arguments are logical or not may not matter. The fact is that laws do vary, and often the power of the law is based on a judge's interpretation. Judges have been known to make rulings that don't necessarily demonstrate a strong understanding of technology or such logic. Advice is not being given here about whether or not a honeypot is recommended, or how to implement or utilize a honeypot. However, advice is hereby given that if a honeypot is going to be used, potential legal ramifications may, at the very least, be worth considering/contemplating.

[#hop]: hop

Whenever an IP (either IPv6 or IPv4) packet goes through a router (and, therefore, starts to get transmitted onto a different subnet), this is referred to as a “hop”. Whenever this happens, the TTL value is decremented.

[#host]: host

A “host” refers to a device on a network.

  • RFC 871: page 2 refers to “computer systems”, that are “usually general-purpose”, are “usually called Hosts.” They are attached to the network, communicating “for the purpose of achieving resource sharing among the participating” computers.
IP hosts

When discussing devices that use an Internet Protocol (IPv4 or IPv6), a specific definition of “host” is commonly used, many of the specific documents.


A device on a network that does not forward packets.

Here are some examples of documents that use this term:

  • RFC 1256: “ICMP Router Discovery Messages”, section 1 uses the terms “router” and host”. (It doesn't use the term “node”, found commonly in newer documents. Instead, if uses the term “system”.)
  • Part of the definition from RFC 1883: (IPv6) section 2: “Terminology” provides a concise definition that is quite straightforward: “any node that is not a router”. (The definition is somewhat muddied by the fact that “node” uses IPv6 as part of the definition, which happened since that document is focused on IPv6. It is, in fact, the original RFC document providing the IPv6 standard.) RFC 4861: section 2.1 does the same sort of thing, described slightly further by the glossary entry for node which may also provide some other references which may also define the word “host”.
  • RFC 793: TCP refers to "the host computer", and uses the term "host" regularly. Specifically, RFC 793 page 80 starts the definition of “host” simply with the sentence: “A computer”.
    • This may be one of the earliest definitions of the word “host&Rdquo;. RFC 1009 section 1 says, “General background and discussion on the Internet architecture and supporting protocol suite can be found in the DDN Protocol Handbook” ... “and ARPANET Information Brochure”, and provides references to some documents including RFC 980: Protocol Document Order Information described the process of ordering information, such as the 1985 Defense Data Network (“DDN”) Protocol Handbook, which sold for over $100 (in early 1986... when $100 was generally worth more than newer years thanks to the economic effect of inflation).
  • Also defined by IETF RFC 2460 (IPv6: Section 2: “Terminology”.
  • RFC 791: Internet Protocol (version 4) uses the term “host” extensively, although it does not provide a specific definition. (Apparently the authors were so familiar with the term that they just assumed it was common enough that they did not bother documenting a clear, precise definition.)
  • RFC 1122 (“Requirements for Internet Hosts -- Communication Layers”) page 6, section 1.1.1: “Internet Hosts” says, “A host computer, or simply "host," is the ultimate consumer of communication services.  A host generally executes application programs on behalf of user(s)”... “An Internet host corresponds to the concept of an "End-System" used in the OSI protocol suite” (A reference is then made to the document which is RFC 995, which does use the phrase “end system” quite a bit.) RFC 1122 is considered to be part of a pair, with the “companion” being RFC 1123: Requirements for Internet Hosts -- Application and Support.

Similiar/related terms include: router (for a device that does forward packets), and node (of a network).

[#hzabbr]: Hz
An abbreviation for hertz.