Python language
GIL (Global Interpreter Lock)
A lock in standard CPython ensuring only one thread executes Python bytecode at a time.
Why interviewers ask about it
Do not stop at 'Python can't do parallelism'. Say: on a default build the GIL applies, so use processes for CPU-bound work. Then add that the free-threaded build (PEP 703) removes it - experimental in 3.13, officially supported in 3.14 - and that removing it does not make your own data structures thread-safe.
Related terms
This term is part of the free Python Full-Stack interview preparation module - browse the full glossary for every definition.