Abbreviation for topography/topographical map. This is a drawing or photo usually accompanied by a description of the route. It depicts the line the climb takes, bolts (if there are any), belay stations (if it's multiple pitches) and some prominent features, such as shrubs or flakes.
A topo is a guide for a crag or climbing area. It gives details of the grade of each of the climb. It includes the length of the climbs and most importantly how to get to the area of the climbs, and where exactly each climb starts.