In jiu jitsu, tapping your opponent or the mat during a match indicates defeat, a silent "you got me." You can also verbally "submit" by saying or yelling the word "tap." Despite the tap signifying defeat during a roll or match, tapping is not a bad thing, and I haven't heard anyone explain this better than Keith Owen:
I'm new enough to jiu jitsu to clearly remember my mentality when I first started training. Every roll was a fight, everyone else on the mats an opponent, and if I was just able to make enough people tap then maybe the instructor would see how awesome I was and I'd get my black belt in no time.
One of the beauties of this art is that most people (there are exceptions of course) will quite quickly learn to put their ego's in check. The reason is, you can't really fool others in jiu jitsu. During a roll your weaknesses are quickly exposed, especially when rolling with more advanced people. Refusing to tap or tapping too late will cause you to get put to sleep or to get a dislocated elbow or shoulder.
As a new blue belt I can say I've lost my fear of tapping during training. It's part of the game. If you're all about tapping others then every roll becomes a fight, and who wants to fight every time you get on the mat? This increases the chance of injury for yourself and your training partners and takes the fun out of training.
I'll admit that I felt a certain anxiety during the first few months after I got my blue belt. Was I supposed to not tap to a white belt? Well, it didn't take long for that to happen, and I've actually tapped to several white belts in these last 10 months as a blue belt. But I had to re-evaluate my attitude. Why am I training? To feed my ego, or to become the best jiu jitsu practitioner I can become? If it's reason number 2, which it is for me, then tapping should be welcomed.
Someone that taps frequently more than likely has the following qualities:
1. They are not afraid to roll with more experienced practitioners.
2. They are not afraid to put themselves in dangerous situations in order to learn to survive them.
3. They are more fun to train with because not every roll becomes a fight, they keep it playful.
4. They are not as likely to get hurt, and not as likely to hurt others.
Here's a funny parody clip of an instructor that hasn't mastered the art of tapping, or the humility that comes with it: