When an establishment is full of hot women, who don't necessarily need to be hot.
For it to be Raining Trim said establishment must have a higher percentage of women to men.
Not to be confused with reining trim, when a gentleman is on a particularly hot streak with the ladies and is indeed reining in trim.
'How was the club last night Mr Sanchez?'
'Oh Gary it was awesome, it was just raining trim'