It is a noun or adjective that describes a very close friend of yours that is almost like a brother to you.
Combination of the words negro and bro. By replacing the "gro" with "bro" you remove all doubts about the racism so you can say the word without the fear of offending someone and in the end feeling better about yourself.
As a noun - Whats up nebro, you catch that hockey game last night?
As an adjective - Jared is the best nebro ever he is always willing to go out of his way to do stuff for me.