Green’s Dictionary of Slang

(US campus) a husband; i.e. the nickname for the degree that a woman who goes to college mainly to find a husband is said to be studying for.

1974		oral testimony in Lighter HDAS II 604/2: If a girl goes to college just to get married, she’s studying for her M.R.S.
1981		Eble Campus Sl. Mar. 5: Mrs Degree – marriage degree.
1997		J. Wyland ‘Choosing a man by the size of his wallet’ Daily Trojan 131: 01 14 May 🌐 It surprised me recently to learn how many of my girlfriends admit that finding a wealthy husband is a top reason they decided to go to college. Sure, they wanted their education, but they are really concerned with their MRS. degree.
2002		Indiana Daily Student 13 Nov. 🌐 You shouldn’t feel like if you haven’t found the love of your life, that you have to have a ‘ring before spring,’ or that if you don’t graduate with an MRS degree you’re a failure.