A casual expression not to be confused with actually asking someone out on a date. At times, when you are to pussy to reject someone, u simply say "it's a date" even tho you dont wanna be a part of it.
it's sometimes accompanied with a ;).. BUT it should be read with a sarcastic undertone if the ;) has been added.
It can be interpreted wrong, be careful with how you use this! To avoid misinterpretation, add the ;)
friend nr 1: "OMG my car broke down last night, can you come over and help me, you handy man! and then we can have some beers"
friend nr 2: *thinking I dont want to do this, putting on the fake happy voice* "yeah sure, it's a date ;)
"Wanna go to the library and do some serious studying?"
"Yeah, it's a date!