The Global Interpreter Lock (GIL) is a distinctive mechanism specific to the CPython implementation of Python, which is widely used and considered the reference implementation. The GIL verifies that only one thread can execute Python bytecode at a time within a single Python process. The purpose of the GIL is to simplify memory management and protect critical internal data structures in Python. It guarantees the thread safety of operations like modifying object reference counts, which is important for C Python's memory management strategy based on reference counting.
However, the GIL has implications for multi-threaded Python programs, especially those that are CPU-bound. Due to the GIL, simultaneous parallel execution of multiple CPU-bound threads is not possible, as only one thread can execute Python bytecode at any given moment. Consequently, the performance of CPU-bound tasks in CPython may not scale well with the number of threads.