> What does it mean for a "thought" to be computable?

Well, given our scientific knowledge it's a molecule-level (only important to disregard quantum physics to make the case easier) physical/chemical process, that we should in principle be able to simulate on any other medium, including a Turing machine.

Nonetheless, I can accept the definition of math where it's about "truths" and truths can obviously exist without being computable.