Noun, abbreviated from 'Homoeroticism, Yay!' The phrase originated from the television programme 'Buffy the Vampire Slayer,' and is used most commonly in various
internet fandoms. It can also be an exclamation of
glee.
The word is used to describe a homoerotic or homoromantic subtext between
two characters, generally on a television show. Where one sees HoYay is, of course, extremely subjective, though in some cases it can be canon, not just subtext, as in the episode of 'Angel' wherein
Spike says 'Angel and I were never intimate... apart from that one time.'