* Literally, the eye of a codfish: Cod, like other fish, have eyes. In culinary contexts, the eye is sometimes removed before cooking the fish, but it is technically part of the fish's anatomy.
* A term used to describe a specific appearance of cooked cod: When cod is cooked perfectly, the flesh will separate easily into large, moist flakes. Some people describe the appearance of these cooked flakes as resembling the "eye" of a cod, characterized by a pearly white color and a slightly translucent look.
* Figuratively, to do with poor eyesight: Colloquially, cod eye might be used to describe someone with poor eyesight.
Without further context, it's hard to know exactly which meaning is intended, but the first two are the most common.