There've been a few threads on this subject. The consensus seems to be that gapers are people who ride around totally oblivious to the fact that there are other people on the mountain. Gapers will ride (or ski) right across a jump as someone is approaching it, or they'll come in from the side, ride up to the lip, and stop to admire the view. Or they'll decide to take a rest break right in the middle of the landing. Or a group of them will stop several across right at the narrowest part of the run.
Basically, these are the people who drive slow in the fast lane, park their shopping buggies crosswise in the narrowest part of the aisle, stop right at the exit of the escalator to think, etc.
Even if you're a beginner, if you put some reasonable effort into basic courtesy and being aware of what other people are trying to do, you're not a gaper.
Someone else can do 'poser'.