An operating system concept that refers to the combination of a program being executed and bookkeeping information used by the operating system. Whenever you execute a program, the operating system creates a new task for it. The task is like an envelope for the program: it identifies the program with a task number and attaches other bookkeeping information to it.
In most operating systems, there is a one-to-one relationship between the task and the program, but some operating systems allow a program to be divided into multiple tasks. Such systems are called multithreading operating systems.
The terms task and process are often used interchangeably, although some operating systems make a distinction between the two.