A Thread ID is a unique identifier assigned to a specific thread within a computer program. Threads are the smallest units of processing that can be scheduled by an operating system, allowing multiple tasks to run concurrently. The Thread ID helps the operating system and developers manage and track these threads efficiently. In programming, each thread created in a process is given a Thread ID to distinguish it from other threads. This identification is crucial for debugging, resource management, and ensuring that tasks are executed in the correct order. Tools and libraries often provide functions to retrieve or manipulate Thread IDs, enhancing overall program performance.