Tap bass is essentially what it infers; tapping on the bass. Instead of fretting the notes normally with your left hand, you press or 'tap' the note you want on the fretboard with your right hand. Then you get into two handed tapping which also is just what it says; tapping with both hands.
This is all tapping really is. I know it sounds simple but it can be very frustrating for someone just learning.
You can hear examples of this from Stu Hamm, Victor Wooten, and even Les Claypool to see what tones it produces.
The song "Linus and Lucy" is two hand tapping and would be a good example, as would the song "DMV" or "Jerry Was A Racecar Driver" by Primus.
I'm absolutely sure if you do a search for 'tap' or 'tapping', you'd find enough information to keep you busy for days.
Hope this helped out a bit.
Alex
