WTO is an acronym which stands for "We The Opps." Opps is slang for opposition. This slang is popular in Chicago, IL. Gang members often use that acronym to let others know that they're the opposition and they're not hiding. Lil Jay mentions this slang in his song "Bars of Clout 2," in which he raps "WTO we the opps, clout boyz you know we the gang."