Defining the term “theory” is not so easy. But one thing is certain: If you want to deal with theory in the science theory, you cannot ignore a man: Karl Popper.
Popper defines theory as “universal statements,” which together form a “net” with which the world can be “captured.”
In the original, the wording makes a little more sense: Theories are “universal statements” used to cast a net to “catch” the world. (Popper, 1959).
A theory should therefore claim to contribute general statements (universal statements) about phenomena (the world) so that the world can be better explained or understood. Specific statements that are only correct in a certain situation are therefore not suitable as a theory.
A theory often only looks at a section of reality. This is often represented as a model.