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Unit of execution or work in software

In computing, a task is a unit of execution or a unit of work. The term is ambiguous; precise alternative terms include process, light weight process, thread (for execution), step, request, or query (for work). In the adjacent diagram, there are queues of incoming work to do and outgoing completed work, and a thread pool of threads to perform this work. Either the work units themselves or the threads that perform the work can be referred to as "tasks", and these can be referred to respectively as requests/responses/threads, incoming tasks/completed tasks/threads (as illustrated), or requests/responses/tasks.

In the sense of "unit of execution", in some operating systems, a task is synonymous with a process, and in others with a thread. In non interactive execution (batch processing), a task is a unit of execution within a job, with the task itself typically a process. The term "multitasking" primarily refers to the processing sense – multiple tasks executing at the same time – but has nuances of the work sense of multiple tasks being performed at the same time. In the sense of "unit of work", in a job (meaning "one off piece of work") a task can correspond to a single step (the step itself, not the execution thereof), while in batch processing individual tasks can correspond to a single step of processing a single item in a batch, or to a single step of processing all items in the batch. In online systems, tasks most commonly correspond to a single request (in request–response architectures) or a query (in information retrieval), either a single stage of handling, or the whole system wide handling.

The term task is used in the Linux kernel (at least since v2.6.13, up to and including v4.8) to refer to a unit of execution, which may share various system resources with other tasks on the system. Depending on the level of sharing, the task may be regarded as a conventional thread or process. Tasks are brought into existence using the clone system call, where a user can specify the desired level of resource sharing.