Thread Control Block (TCB) is a data structure in an operating system kernel that contains thread-specific information needed to manage the thread.
[1] The TCB is "the manifestation of a thread in an operating system."
An operating system keeps track of the thread control blocks in kernel memory.
[2] An example of information contained within a TCB is: 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.