The act of spending the night with another person (male or female) that would allow that person spending the night to go to sleep and wake up next to the person they desire to spend the night with.
"Trevor often asks Brittney if he can spend-the-night but rarely does she accept his request. She will often reply with maybe
or will ignore his attempt and change the subject" See also hard to get
The equivilant of a slumber party or sleepover but for older ages like high school or college. (STN)
Alex: Are you trying to STN tonight?
Isabella: Duh, every night is Spendthenight.
a seemingly innocent way to refer to a sleepover between potential love interests or sexual partners
Oh nothing," says Arnold with a smile and a wink, "I just took her out to dinner and we had a spend-the-night afterwards.