While Jon Gretar is right about Erlang, the programming language/runtime system, I believe Adso is asking about the measurement unit.

An erlang is a measurement unit describing the traffic volume on a voice network in 1 hour. Basically, you take the number of calls made within a particular time frame (1 hour), the duration of those calls, then multiply them and divide by 60 (60 minutes in 1 hour).

So, let's say that on a particular network, there are 50 calls made. For simplicity's sake, let's say that all calls were 10 minutes (or the average call duration was 10 minutes -- it works out the same).

So then, 50 calls, 10 minutes each. 50 x 10 = 500 minutes of calls within that one hour. 500/60 = 8.33

Therefore, the erlang for this voice network for that particular hour is 8.33.

Erlang is a general-purpose programming language and runtime system made by Ericsson. Its original main purpose was as a fault tolerant and distributed system to develop phone switches.

While still in use in various telephoning applications it has recently been popular in general programming because of its concurrent fault-tolerant nature.