I think (although please jump in to correct me if I've got this wrong) that a hybrid is a nappy that can be used in more than one way. So Grovia hybrids have several different types of soaker pads that snap in or can be used with disposable soaker pads too, so the shell acts as a wrap. Likewise with CB nappies they have disposable inserts than tuck under the flap so the nappy is the wrap.
A Mama Knows are sometimes called hybrids because they have a waterproof layer so can be worn for a while (if you don't have a heavy wetter!) without a wrap so it's like an AIO, or can be a 'normal' fitted nappy with a wrap.
That's my understanding of hybrid anyway.