Initialism of Harvard/Yale/Princeton.

(Internet slang) Shaking my head (used to show that one does not approve of something or cannot believe it). / (Internet slang) Scratching my head (used to convey confusion or incredulity).

Initialism of emissions reduction currency system. / (medicine) Initialism of elective repeat cesarean section.

Under the surface of a liquid; sunk. / Deeply involved.