Theory

noun

1. A description of an event or system that is considered to be accurate.
2. Mental conception; reflection, consideration.
3. A coherent statement or set of ideas that explains observed facts or phenomena and correctly predicts new facts or phenomena not previously observed, or which sets out the laws and principles of something known or observed; a hypothesis confirmed by observation, experiment etc.
4. The underlying principles or methods of a given technical skill, art etc., as opposed to its practice.
5. A field of study attempting to exhaustively describe a particular class of constructs.

   "Knot theory classifies the mappings of a circle into 3-space."