In computer programming, await is a feature found in C# 5.0, Python 3.5, in an experimental extension for Scala, and more recently JavaScript that allows an asynchronous, non-blocking method call to be performed in a similar way to an ordinary synchronous method call.
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While a casual reading of the code would suggest that the method call blocks until the requested data is available, in fact it does not.
In C#
This is an example:
In Scala
In the experimental Scala-async extension to Scala, await is a "method", although it does not operate like an ordinary method. Furthermore, unlike in C# 5.0 in which a method must be marked as async, in Scala-async, a block of code is surrounded by an async "call".
How it works
In Scala-async, async is actually implemented using a Scala macro, which causes the compiler to emit different code, and produce a finite state machine implementation (which is considered to be more efficient than a monadic implementation, but less convenient to write by hand).
There are plans for Scala-async to support a variety of different implementations, including non-asynchronous ones.
In Python
Python 3.5 has added support for Async/Await as described in PEP0492 (https://www.python.org/dev/peps/pep-0492/).
In JavaScript
The initial spec for the ES7 (ES2016) feature can be found here: https://github.com/tc39/ecmascript-asyncawait.
Here's an example (modified from this article):