In cooking, “to dress” is to add salad dressing to a salad, or to prepare a whole animal or aquatic life for cooking.
To dress an animal, usually the head and feet are chopped off and discarded, any feathers, fur or fins are removed, and the inside organs are removed as well. Things that are usually dressed are smaller critters that are usually eaten whole: chickens, fish, octopus, etc. The word isn’t generally applied to larger things such as cows, pigs or whales.
A salad that has had dressing applied, or a (formerly) living creature that has been cleaned in preparation for cooking.
“Aliñar” in Spanish refers to dressing a salad. “Aliño” refers to a salad dressing.