An algorithm is a step-by-step procedure that guarantees a solution to a particular problem if one exists. It is methodical, finite, and defined clearly enough that a computer—or a careful human—can follow it without improvisation.

In cognitive psychology the term is used to contrast with heuristics. An algorithm for solving an anagram might be to generate every possible rearrangement of the letters until the word appears; the method is guaranteed but slow. A heuristic might be to try common prefixes and suffixes first; it is faster but can fail. People rarely use pure algorithms for everyday problems because the search space is often too large and time is limited.

In computer science algorithms are the core of programming. Sorting, searching, pathfinding, and encryption all rely on carefully designed procedures whose efficiency can be analyzed mathematically. The same formal spirit has entered psychology through computational models of perception, memory, and decision making.

When a process is described as algorithmic, the claim is that every step is specified and the outcome, given enough resources, is assured.