Bassai shō is an advanced black belt kata.
This is one of the kata that can be selected for the 2nd Dan Black Belt examination. 

Bassai shō (披塞小) (to storm the fortress minor)

Many Dojo refer to Sho as minor and Dai as major, my Sensei explained to me that another story about Passai, was that there were two Passai kata, one was Master Tawada (Passai/Bassai) and the other was the Master Matsumura (Passai/Bassai), one became sho and one became dai.

Bassai Sho is recognized by the unique foot sweep, outside block, double strike combination and the two last moves of this shotokan kata which involve takedowns.