Context will define the use of theory. In the context of exams for example, you take your theory exams and a practical exam, which in the case of a driving test is actually driving with an examiner observing your performance.
In the case of something like evolution, it means a hypothesis. I guess the reason why something like evolution remains a ‘theory’ is not that it lacks proof but it is that it continues itself to evolve and to be found to be deeper than originally thought.