Many definitions of a task have been proposed in computer literature. Unfortunately, none of these definitions encompasses all facets of the concept in a manner which is operating system independent. Several of the more common definitions are provided to enable each user to select a definition which best matches their own experience and understanding of the task concept:
a "dispatchable" unit.
an entity to which the processor is allocated.
an atomic unit of a real-time, multiprocessor system.
single threads of execution which concurrently compete for resources.
a sequence of closely related computations which can execute concurrently with other computational sequences.
From our implementation perspective, a task is the smallest thread of execution which can compete on its own for system resources. A task is manifested by the existence of a task control block (TCB).
RTEMS ITRON 3.0 API User's Guide