(a word of obscure derivation, says the OED, perhaps connected with coal) had from early times the primary meaning of a rasher of salt bacon, to be fried, often with eggs; ‘a peculiarly British fashion of eating bacon, not known elsewhere in Europe’. The comment is from
Later, the term came to have the more general meaning of a slice of meat. Hannah glasse’s recipe for Collup and Eggs, and her recipes for Scotch Collop, illustrate this development in the meaning of the word. Scotch collops were a well-known dish from the 17th to the 19th centuries, although the manner of preparing them changed with the passage of time.