To post up is to chill somewhere. For example, someones home, a street, or any other location.

not just a pose... but a lifestyle. postin up is a privilege not a right. the origin of postin up can't officially be traced but it was believed to be started around the year 3000 B.C. when one posts up they find themselves in a state of relaxation, most of the time arms are folded and back is to a wall. if a wall is not present to "post" on, the postee can still "post up" with their arms folded taking a moderate athletic stance. a postee can not "post up" for more than 1 minute and 17 seconds at a time, violations of this essential rule can result in a loss of post privileges for the rest of said day.

The act of going to a public place usually a gas station, street corner, by a deli or convenience store and hanging out and standing in a way so people will know you holding / selling drugs.