A ricer is a person that buys a lesser expensive car like a Honda, Acura, Nissan, or Mitsubishi, etc. and then buys modifications for it such as engine mods to increase performance or body kits to make their car look more distinctive. Ricer isn't exactly a look, but more of an attitude. Most ricers believe their car to be speed rockets because of what they've done to it or because of the way they make it look. A ricer usually has little idea of what he's actually doing and will generally buy the largest exhaust pipe available to make his car sound louder.

It's really more about the look and sound of the car than the actual performance.

If that didn't explain it well enough then I could go more indepth or try a different angle on the topic. A person can modify their car without being a ricer. But the term ricer came about because it refered to smaller Japanese made cars that were less expensive that people on a budget could buy and try to make faster.