When you fuck your partner in the ass with their underwear still on, pushing the fabric inside the anus.
When you get fucked in the ass while your underwear is still on pushing the fabric inside your anus.
The Galush: The sexual definition is self explanitory.
This can also be used as an expression. eg when you think you have a good deal, but then you relize that you been screwed over because of a rediculous double talk. You say, "I think I just got Galushed!?" or "I've been Galushed!"