Green’s Dictionary of Slang

1. (US campus) one who is good at seducing others.

1963

Mad mag. Jan. 31: The one sitting in the front on the right (who is usually the best ‘make-out’) [...] leans out as they pass females, and shouts clever, daring pick-up phrases .

2. (US, also making-out) romantic and sexual behaviour; often attrib., e.g. make-out session.

1970		Meyer & Ebert Beyond Valley of the Dolls [film script] Am I interrupting something? [...] Only a little make-out session .
1972		E. Grogan Ringolevio 86: Walking with chicks for a Sunday stroll and make-out in the park.
1978		R. De Christoforo Grease 182: We went into a heavy, juicy make-out.
1999		Guardian G2 24 June 2: We had a sort of making-out session.
1999		Indep. Rev. 18 July 12: From the age of 14, she went to ‘make-out parties’, where ‘you invited a group of boys and girls, and you turned out the lights, and you played ... games.’.
2005		Mad mag. Nov. 20: After a really steamy make-out session, don’t ask her to give you extra credit.
2023		(con. 1962) J. Ellroy Enchanters 73: The big new thing? It’s the prearranged makeout date.