An enclosing seki is a seki which does not evolve from any cut but where the enclosing group cannot capture
- because of shortage of liberties
- because it would leave a dead shape AND the inner group cannot almost fill without leaving a live shape.
Both of these varieties are probably most common in the corner. Simplest examples:
Probably the biggest difference is that the shortage of liberties variety (which, one might note, all cutting sekis are) can be used as ko threats by either player. The dead shape variety cannot, except: a) if there are two inside and no outside liberties (in which case you can consider it a special seki of both types, and only the player of the inner group can use it as a ko threat) or b) if there is some semeai or other seki going on outside (in which case one or the other, or either player may use it as a ko threat, depending on the circumstances).
A more convoluted example: