No Gi is a modern martial arts uniform, usually the top is a rash guard and bottom are shorts. It is used for Brazilian Jiu Jitsu training, wrestling, weight-lifting / conditioning, catch fighting, and more.
As opposed to the gi, this uniform allows competitors or practitioners to fight without the need to worry about gi-based submission techniques. No belt is used in no gi Brazilian Jiu Jitsu, however some schools differentiate amongst students with rank by showing colored rash guards or colored shorts.
The following are examples of Brazilian Jui Jitsu Rashguards: