A single thread of execution that runs concurrently with other threads in a preemptive multitasking environment. Each thread can execute independently, but requires context switching managed by the operating system. Parallel threads can improve performance in multi-core systems but introduce challenges such as synchronization, race conditions, and increased CPU overhead. In robotics, threads are used for tasks that must run truly concurrently, such as high-frequency sensor data acquisition or communication with external systems.