ETYM French théorie, Latin theoria, Greek thea a beholding, spectacle, contemplation, speculation, from horan to see, view. Related to Theater.
In science, a set of ideas, concepts, principles, or methods used to explain a wide set of observed facts. Among the major theories of science are relativity, quantum theory, evolution, and plate tectonics.
1. A belief that can guide behavior.
2. An organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena.