Meaning

1. theory (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)
2. theory (someone's personal view on something)
3. theory (branch of a specific scientific discipline that deals with the basic concepts and principles of that discipline)
4. theory (a hypothesis or conjecture)
5. theory (the underlying principles or methods of a given technical skill, art etc., as opposed to its practice)
6. (obsolete) sending of state-ambassadors