A chord is a concurrency construct available in Polyphonic C♯

Polyphonic C sharp

Polyphonic C# is an extension of the C# programming language.It includes a new concurrency model in which objects can have both synchronous and asynchronous methods...

 and Cω inspired by the join pattern of the join-calculus

Join-calculus

The join-calculus is a process calculus developed at INRIA. The join-calculus was developed to provide a formal basis for the design of distributed programming languages, and therefore intentionally avoids communications constructs found in other process calculi, such as rendezvous communications,...

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Synchronicity

Cω defines two types of functions synchronous and asynchronous. A synchronous function acts like a standard function in most Object-Oriented Language, upon invocation the function body is executed and a return value may or may not be returned to the caller. An asynchronous function acts similar to a function that returns void except that it is guaranteed to return immediately with the execution being done in a separate thread.

Chord Definition

A chord is a function body that is associated with multiple function headers and cannot execute until all function headers are called.