The question asks it all really. When referring to a master's degree, do you use an apostrophe or not? That is, is it "a master's" or "a masters"?
I always use "master's degree". You may want to read this article about this topic. Below are some important parts of it which I found very useful.
Masters Degree or Master’s Degree? by Maeve Maddox
To answer this question, I’ve consulted the MLA Handbook for Writers of Research Papers, and some university dissertation guidelines.
Speaking generically, you would write master’s degree:
- Jack has finally earned his master’s degree.
Speaking of a specific degree, you would capitalize Master:
- He holds a Master of Fine Arts from State University.
When it comes to abbreviating academic degrees, you’d better check the style book that governs your work.
For example, here is what the guidelines say on the site of Ohio University:
- “Use periods when abbreviating academic degrees. Ex. Dr. Bond received her A.B., M.A., and Ph.D. from the University of Pennsylvania.” –Ohio University
Northeastern University, like the MLA guide, prefers to drop the periods:
- “Punctuating degrees: Do not include periods in degree abbreviations. [Ex. BS, BA, MA, PhD] The single exception is Hon. for Honorary.” –Northeastern University
NOTE: Not all universities use the same abbreviations for the master’s degree:
- Examples of the reversed usage include Harvard University, the University of Chicago and MIT, leading to the abbreviations A.M. and S.M. for these degrees. The forms "Master of Science" and "Master in Science" are indistinguishable in Latin, thus MSci is "Master of Natural Sciences" at the University of Cambridge. –Wikipedia