Cilk is a programming language designed for parallel computing, which allows developers to write efficient code that can run on multiple processors simultaneously. It was originally developed at MIT and is known for its simplicity and ease of use, enabling programmers to focus on the logic of their applications without getting bogged down by complex threading issues. Cilk uses a unique model based on the concept of "spawn" and "sync" to manage tasks. When a function is called with the "spawn" keyword, it can run concurrently with other tasks, while "sync" ensures that the program waits for all spawned tasks to complete before proceeding. This approach helps optimize performance in multi-core systems.