This is slang, and very informal. "Holla´" comes from "Holler" which means ´to shout´, but is rarely used in that literal sense. "Holla´ at you boy" - is sort of a greeting. To "holla´" at someone could be to say hello to someone, acknowledge someone, call someone over. A similiar expression: "I´d like to give a shout out to my friends" meaning that the speaker wants to send out a greeting to his friends. "Boy" could be interpreted as being an african american, but it doesn´t have to be. This sort of language is very common in the hip-hop/RnB/soul industry.

1- to call or catch up with. yo you going to the cub? "yea" aight then holla at ya boy when you get there. http://www.urbandictionary.com/define.php?term=holla%20at%20ya%20boy

What is the context of this? This type of slang is sometimes used by American negroes or people living in the southern states of America. "holla at you boy"= to yell at a boy/man Also during the time negroes were kept as slaves in America, men were often called "boy" by their employers.

I think that language mist be ebonics.