Traditional Brazilian Jiu-Jitsu is performed while wearing a kimono or "gi." A gi is made from resilient cloth comprised of pants, a jacket, and a belt to hold the jacket closed. The gi was originally used in Japanese jiu-jitsu and judo as a durable representation of the clothing that a Japanese man would wear.
It is well within the "rules" of grappling with the gi to use the cloth for controlling grips.
"No-Gi" grappling is done without the gi. Most people wear shorts and a t-shirt or rashguard. The "rules" set being that you're not allowed to use the cloth for controlling grips.
No-gi grappling is more akin to what you would see from wrestlers or mixed martial artists.
Because there is no cloth to grab, no-gi comes with it's own controlling grip sets, techniques, and maneuvers that are similar to traditional Brazilian Jiu-Jitsu. The point being that in a street encounter, you may not have the additional clothing to grab on to. And, if you are interested in sport grappling or mixed martial arts, you must have high level no-gi grappling.
Call or visit the academy for more information!