Synonymous with 'a lot', often referring to almost all of something.
My shit-pants partner and I ate a large portion of a strawberry swirl cheesecake, leaving only a cock-shaped piece left in its plastic container. This ultimately lead to the statement that we ate 'all but a cock' of the cheesecake.
1) "Wow, we ate all but a cock of that cheesecake."
2) "I know all but a cock about the female anatomy."