A process is a series of stages in time where the last stage is the product, result or goal.

Processes may be planned or unplanned.

A process planned by humans has a purpose. It is a course of action, or a procedure, to achieve a result, or an end-product. The sequence from start to finish is the plan. A plan may be written, or programmed, or just held in the mind. Examples include building a house, fighting a battle. sowing crops; organising a wedding.

Natural processes are not planned by humans. They are investigated and described. Examples: volcanic eruption, the evolution of the solar system; biological evolution; the melting of ice and other phase changes; the process of development from egg to adult.

Processes often repeat whenever certain conditions hold. Example: car low on petrol/gas, visit garage and refill. Most computer programs are of this type. Processes may be circular: planets revolve around sun; eggs produce chickens, and chickens produce eggs. Rain water flows into rivers, evaporates, and returns as rain.

Processes, especially those which are cyclical, may be subject to feedback. A simple case is a central heating system.