It is a feature that allows each thread to have its own memory space for storing and retrieving data using global allocation indexes. When a thread starts, it is allocated a block of dynamic memory and stores a pointer to this memory in a thread slot.

References:

• https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src/ProcThread/using-thread-local-storage.md

• https://learn.microsoft.com/en-us/windows/win32/procthread/thread-local-storage

• https://learn.microsoft.com/en-us/sysinternals/resources/windows-internals

Thread Local Storage (TLS)