booty call
Hello. I had to look it up in a dictionary myself to make sure I was clear on the definition.
The Urban Dictionary defines it as follows:
A late night summons -- often made via telephone -- to arrange clandestine sexual liaisons on an ad hoc basis.
So basically, someone who knows the other person very well, or even not very well at all, will call someone for a meeting somewhere for a casual sexual encounter.
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