Surreptitious acronym meaning "Consistent Orgasm Giver." More reliable and FAR more skilled than the famed 'booty call' or 'hookup,' less dangerous than 'friends with benefits,' more elegant and less mechanical than 'fuckbuddy.' A cog is the Holy Grail of dependable hook-ups. Use of this term is particularly useful as it is pretty fun to say, lessens the harshness of speaking 'orgasm' aloud in mixed company, and has the appropriate double entendre of 'cogs' in clocks that mesh well and therefore make everything run smoothly.
"It's getting kind-of late. Tryna go to bars?"
"Nah, think I'll just call my cog."
"You two have amazing chemistry! Is he your boyfriend?"
"Hell nah, he's my cog."