Just calling somebody out if you don't know their name.
Or expressing how dumb that action was.
Or telling people how cool the action or thing you're seeing is.

the thing that you don’t have when you’re phones percentage is over 20

It means Hey You.
It is mainly used when addressing an individual in any given situation to get his or her attention.

a streamlined fusion of the salutation "hey, yo" that goes over extremely well with the modern urban entrepreneur.

a response for a very suspect or homosexual comment.

often used as a gteeting in replacement of "hey yo"

This is a Nigerian name of the Yoruba dialect which means 'Joy'. It can be combined with other names.