Opp

common nouns: Opponent; Opposition; Rival

someone who is against or in competition with a person, group, or organization

This term is a slang form of the 3 commonly used synonyms listed above. (note none of these words have the same meaning except they are very synonymous, making the use of the word opp, an acceptable replacement for all 3 in slang terms).

Aye g, there go that opp boy we saw on this block yesterday.

The opps rolled by just now, stay alert.