A ban requires "consensus", and is a formal warning that if violated will lead to sanctions imposed by an Administrator, while a block can be imposed by a single Administrator and prevents editing to some degree, large or small.
A ban requires "consensus", and is a formal warning: if an individual Administrator judges a ban has been violated, without further consultation that Administrator will impose sanctions. A block, on the other hand, can be imposed by a single Administrator and prevents editing to some degree, large or small.