1. <person> Agner Krarup Erlang. (The other senses were named after him).
2. <language> A concurrent functional language for large industrial real-time systems by Armstrong, Williams and Virding of Ellemtel, Sweden.
Erlang is untyped. It has pattern matching syntax, recursion equations, explicit concurrency, asynchronous message passing and is relatively free from side-effects. It supports transparent cross-platform distribution. It has primitives for detecting run-time errors, real-time garbage collection, modules, dynamic code replacement (change code in a continuously running real-time system) and a foreign language interface.
An unsupported free version is available (subject to a non-commercial licence). Commercial versions with support are available from Erlang Systems AB. An interpreter in SICStus Prolog and compilers in C and Erlang are available for several Unix platforms.
Open Telecom Platform (OTP) is a set of libraries and tools.
Commercial version - sales, support, training, consultants. Open-source version - downloads, user-contributed software, mailing lists.
[Erlang - "Concurrent Programming in Erlang", J. Armstrong, M. & Williams R. Virding, Prentice Hall, 1993. ISBN 13-285792-8.]
3. <unit> 36 CCS per hour, or 1 call-second per second.
Erlang is a unit without dimension, accepted internationally for measuring the traffic intensity. This unit is defined as the aggregate of continuous occupation of a channel for one hour (3600 seconds). An intensity of one Erlang means the channel is continuously occupied.