To elaborate on what Jeppoz and Liquid said.. There are basically 2 types of graphics: Raster and Vector. Raster graphics are made up of squares of color known as pixels. Vector graphics are made up of mathematically defined lines that are filled or stroked with color. These lines/shapes can be scaled either up or down with no loss of quality whatsoever. Technically speaking, all graphics you see on a computer are raster graphics, but some of them were made using vectors. Since it's easier to show you what's not raster, I'll give you an example of a vector: Notice the crisp lines, fairly low detail, etc.. There are however some incredibly amazing and detailed vectors that you would swear are photos.. As for the rest of your questions.. Grunge: I can't really show you an example of premade, but, basically, it's anything that you personally didn't make, but use.. Vector I already showed you.. Abstract is kind of vague, but, as far as the whole graphics community on the web goes, this is an abstract: