what does Yo mean?

something you show grade 1 kids before you catch their cheek

It's a word Goober picked up in the Navy.

'i' in spanish

Used as a greeting or to attract attention.
Generally.
The Urban dictionary defines it as shorthand for the word your.
The dictionary of slang defines Yo as an interjection used to get somebody's attention.

a baseball term short for "you're out"

[youtube=https://www.youtube.com/watch?v=b2F5qf7kLqE]