What is the meaning of Opp?

Abbreviation of opposite.

An opponent; an enemy; the opposition.

Any person on unfriendly terms.

Abbreviation of opportunity.

Salaca form of oppõ (“to learn”)

up (away from earth’s centre)

up (to completion)

un- (the inverse of a specified action)

up (away from earth’s centre)

alternative form of upp

an opp (opponent, enemy, especially among criminal gangs)

Source: wiktionary.org