"Masters degree" — capital M or not?

The word "master's degree", used generically, means the degree attained by a master. For example, using it in this sentence is correct:

I received my master's degree from the university last January.

The capitalised form is usually used to refer to a specific master's degree by name:

I received my Master['s] of Science degree from the University of Waterloo last January.

Universities may use any of "Master", "Master's" or "Masters" when naming their specific master's degree, and you should use the same one.