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In computer science, the sleeping barber problem is a classic inter-process communication and synchronization problem between multiple operating system processes. The problem is analogous to that of keeping a barber working when there are customers, resting when there are none, and doing so in an orderly manner.

The Sleeping Barber Problem is often attributed to Edsger Dijkstra (1965), one of the pioneers in computer science.

In psychology, the four stages of competence, or the "conscious competence" learning model, relates to the psychological states involved in the process of progressing from incompetence to competence in a skill. People may have several skills, some unrelated to each other, and each skill will typically be at one of the stages at a given time. Many skills require practice to remain at a high level of competence.

The four stages suggest that individuals are initially unaware of how little they know, or unconscious of their incompetence. As they recognize their incompetence, they consciously acquire a skill, then consciously use it. Eventually, the skill can be utilized without it being consciously thought through: the individual is said to have then acquired unconscious competence.

Hitsuzendō (筆禅道, "way of Zen through brush") is believed by Zen Buddhists to be a method of achieving samādhi (Japanese: 三昧 sanmai), which is a unification with the highest reality. Hitsuzendo refers specifically to a school of Japanese Zen calligraphy to which the rating system of modern calligraphy (well-proportioned and pleasing to the eye) is foreign. Instead, the calligraphy of Hitsuzendo must breathe with the vitality of eternal experience.

Kwangmyong (literally “Bright Light”) is a North Korean "walled garden" national intranet service opened in 2000.

The network uses domain names under the .kp top level domain that are not accessible from the global Internet. As of 2016 the network uses IPv4 addresses reserved for private networks in the 10.0.0.0/8 range. North Koreans often find it more convenient to access sites by their IP address rather than by URL using Latin characters. Like the global Internet, the network hosts content accessible with web browsers, and provides an internal web search engine. It also provides email services and news groups.

Only foreigners and a small number of government officials/scholars/elites are allowed to use the global Internet in North Korea, making Kwangmyong the only computer network available to most North Korean citizens. It is a free service for public use.

The 1983 U.S. Senate bombing was a bomb explosion at the United States Senate on November 7, 1983, motivated by United States military involvement in Lebanon and Grenada. The attack led to heightened security in the DC metropolitan area, and the inaccessibility of certain parts of the Senate Building. Six members of the radical left-wing Resistance Conspiracy were arrested in May 1988 and charged with the bombing, as well as related bombings of Fort McNair and the Washington Navy Yard which occurred April 25, 1983, and April 20, 1984, respectively.

The Aarne–Thompson–Uther Index (ATU Index) is a catalogue of folktale types used in folklore studies. The ATU Index is the product of a series of revisions and expansions by an international group of scholars: Originally composed in German by Finnish folklorist Antti Aarne (1910); the index was translated into English, revised, and expanded by American folklorist Stith Thompson (1928, 1961); and later further revised and expanded by German folklorist Hans-Jörg Uther (2004). The ATU Index, along with Thompson's Motif-Index of Folk-Literature (1932) (with which it is used in tandem) is an essential tool for folklorists.

A sea anchor (also known as a parachute anchor, drift anchor, drift sock, para-anchor or boat brake) is a device that is streamed from a boat in heavy weather. Its purpose is to stabilize the vessel and to limit progress through the water. Rather than tethering the boat to the seabed with a conventional anchor, a sea anchor provides hydrodynamic drag, thereby acting as a brake. Normally attached to a vessel's bows, a sea anchor can prevent the vessel from turning broadside to the waves and being overwhelmed by them.

Early sea anchors were crude devices, but today most take the form of a marine drogue parachute. These are so efficient that they need a tripping line to collapse the parachute for retrieval. Being made of fabric, a sea parachute may be bagged and easily stowed when not in use.

A similar device to the sea anchor is the much smaller drogue, which is streamed from a vessel's stern in strong winds so as to slow the boat to prevent pitchpoling or broaching in an overtaking sea. The fundamental difference between the sea anchor and the drogue is that the drogue will slow the boat while keeping the heading steady, and is intended to be launched from the stern. The parachute anchor is designed to be launched from the bow and effectively stop the boat's progress relative to the current in an open sea.

The Luhn algorithm or Luhn formula, also known as the "modulus 10" or "mod 10" algorithm, named after its creator, IBM scientist Hans Peter Luhn, is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers, National Provider Identifier numbers in the United States, Canadian Social Insurance Numbers, Israel ID Numbers, South African ID Numbers, Greek Social Security Numbers (ΑΜΚΑ), and survey codes appearing on McDonald's, Taco Bell, and Tractor Supply Co. receipts. It is described in U.S. Patent No. 2,950,048, filed on January 6, 1954, and granted on August 23, 1960.

The algorithm is in the public domain and is in wide use today. It is specified in ISO/IEC 7812-1. It is not intended to be a cryptographically secure hash function; it was designed to protect against accidental errors, not malicious attacks. Most credit cards and many government identification numbers use the algorithm as a simple method of distinguishing valid numbers from mistyped or otherwise incorrect numbers.

Xsnow is a software application that was originally created as a virtual greeting card for Macintosh systems in 1984. In 1993, the concept was ported to the X Window System as Xsnow, and was included on a number of Linux distributions in the late 1990s.

An emirp (prime spelled backwards) is a prime number that results in a different prime when its decimal digits are reversed. This definition excludes the related palindromic primes. The term reversible prime is used to mean the same as emirp, but may also, ambiguously, include the palindromic primes.

The sequence of emirps begins 13, 17, 31, 37, 71, 73, 79, 97, 107, 113, 149, 157, 167, 179, 199, 311, 337, 347, 359, 389, 701, 709, 733, 739, 743, 751, 761, 769, 907, 937, 941, 953, 967, 971, 983, 991, ... (sequence A006567 in the OEIS).

All non-palindromic permutable primes are emirps.

As of November 2009, the largest known emirp is 10¹⁰⁰⁰⁶+941992101×10⁴⁹⁹⁹+1, found by Jens Kruse Andersen in October 2007.

The term 'emirpimes' (singular) is used also in places to treat semiprimes in a similar way. That is, an emirpimes is a semiprime that is also a (distinct) semiprime upon reversing its digits.