Basically, it is a description of sexual nature that could involve any of acts: when a dominant person takes a submissive role but still remains in charge while the actual submissive person takes a dominant role but still takes orders. Guy 1: So I heard Derek let you top last night?
In its basic, literal sense, it means exactly what it says. Person A: I heard you fucked Riley last night.
Guy 1: Ah, clearly he was topping from the bottom. A dominatrix is said to "top from the bottom" when she lets her submissive tie her up and perform oral sex on her, but all the while she is telling him how she likes to be licked and he does it how she says to. When a top just ain't hittin' it right, and needs some guidance and expertise so the bottom gives their own input on how they like it.
The person on the bottom is leading the top, thus technically topping from the bottom. Person B: Yeah, he wasn't a really expirenced topso I had to start topping from the bottom. Guy 2: Yeah, but even though he was bottominghe still had most of the control. Topping from the Bottom. Topping From The Bottom.