YOLO is a term used by many teens
Same as LOL, GTG, BRB, TTYL, TBH
These terms all mean something in their own special way
LOL meaning Laugh Out Loud
GTG meaning Got To Go
BRB meaning Be Right Back
TTYL meaning Talk To You Later
TBH meaning To Be Honest
Many adults are completely oblivious as to what their teens are talking about
Others think they know what their teens are talking about
When they really don't  
Such as LOL meaning Laugh Out Loud when some parents think it means Lots Of Love
This can take a very big, bad turn if you use them the wrong way

Mom: How was your day?
Daughter: My Friends Mom just died!
Mom: ***! LOL!
Daughter: MOM!!!!!
Mom: What?
Daughter: It's not funny that her mom died!!!
Mom: I never said it was.
Daughter: Then What did you mean?
Mom: I meant Lots Of Love
Daughter: OOOHHH

So you can see how there can be a little misconception when using these terms and some people may not know what they mean or how to use them