Acmegenesis is an historic term for orgasm, or the onset of sexual climax. The term comes from a combination of the word “acme” meaning "height of" and “genesis” which means "creation" or "beginning." The orgasm is often considered to be the beginning of life or creation, which helps explain the term.
Acmegenesis has largely been replaced in the modern vernacular by more contemporary terms like climax or simply, orgasm.