Red Onion
Red onion is a purple-skinned onion with a sharp bite when raw and a sweeter flavor when cooked. It is used chopped, sliced, pickled, roasted, or sauteed.
Identity
Sharp allium
Adds onion flavor with a little color.
Use red onion when a recipe can benefit from its color and sharper flavor. Cooking softens the bite, while raw or lightly cooked red onion stays more assertive.
Wikimedia Commons
Reference image
Red Onion reference image.

Source: Wikimedia Commons
Used In Recipes
Substitutions
Acceptable
Avocado -> Red Onion
Optional garnish: avocado, red onion, shredded cheese or sour cream
The source lists this as an alternative in the same ingredient row.
Source: BEEF CHILI RECIPE