Closure, Coroutine, Idempotent and Reentrancy

Closure - First class function that have access to free variables in a lexical environment
Coroutine - is a subroutine that have multiple entry points for suspending and resuming at certain locations - ex, C# we can use yield.
Idempotent - is an operation that be called multiple times without changing the result beyond initial application - ex, Cancel Order/Change address are idempotent, but Placing an order is not.
Reentrant - a re-entrant block of code is one that can be entered by another actor before an earlier invocation has finished, without affecting the path that the first actor would have taken through the code. That is, it is possible to re-enter the code while it's already running and still produce correct results.
Virtual Machine - Software emulation of a computer, two types - System VM and Process VM. Process VM provides portability and flexibility, and is bound to a single process. Loads when process load, and unloads when process goes out of scope. Process will be restricted to the resources/abstraction provided by VM. CLR is an example of Process VM