A UNIX process is a program in execution, that is, an instance running in an execution context.

Generally, especially in microkernel-based systems, the kernel's idea of a task is not as encompassing as a UNIX process, and will use additional effort to enhance the kernel's primitive to a full-fledged UNIX model. In the GNU/Hurd, processes are based on Mach tasks, but are enhanced by the glibc.