Sometimes it is useful if we can capture the state of the application,
its stack of function calls, which includes local variables, the global
variables and the program counter, and save them into an object. If
this object would give us the ability to restart the processing from
the point stored in it.
A continuation is exactly the type of object that we need. Think of a
continuation as an object that, for a given point in your program,
contains a snapshot of the stack trace, including all the local
variables, and the program counter. You can not only store these
things in the continuation object, but also restore the execution
of the program from a continuation object. This means that the stack
trace and the program counter of the running program become the ones
stored in a continuation.
Continuations are powerful concepts from the world of functional
languages, like Scheme, but they are becoming popular in other
languages as well.