I'm afraid that you'd flunk your 8th grade Science exam with that answer.
From Wikipedia - not that they are the be-all and end-all of everthing, but in this case it's well put:
In science a theory is a testable model of the manner of interaction of a set of natural phenomena, capable of predicting future occurrences or observations of the same kind, and capable of being tested through experiment or otherwise verified through empirical observation.
A conjecture would be equivalent to a guess. The next step up is hypothesis, which would be a conjecture that is testable through some means. If the test is conducted and the hypothesis is not disproved, then it is a theory. Theories are repeatedly subjected to tests. As long as no test contradicts the theory, or as long as any such contradiction can be resolved through modification of the theory that does not then cause it to contradict any previous test, the theory remains valid.
There is no particular requirement that a theory be reducible to mathematical expression.
you can’t test something that has no structure