https://en.wikipedia.org/wiki/Thread_control_block

Thread Control Block (TCB) is a data structure in the operating system kernel which contains thread-specific information needed to manage it. The TCB is "the manifestation of a thread in an operating system".

An example of information contained within a TCB is:

• Thread Identifier:Unique id (tid) is assigned to every new thread
• Stack pointer: Points to thread‘s stack in the process
• Program counter
• State of the thread (running, ready, waiting, start, done)
• Thread‘s register values
• Pointer to the Process control block (PCB) of the process that the thread lives on

The Thread Control Block acts as a library of information about the threads in a system. Specific information is stored in the thread control block highlighting important information about each process.

Thread control block & thread