A hood is a protective covering. It could be a car hood protecting the engine or your car or it could be the hood on your coat protecting your noggin.
Your favorite sweatshirt might have a hood, as well as your fur-lined winter coat and your insulated hood for scuba diving. Other things with a similar protective quality are also called hoods, like the metal vent cover over your stove, the cover on your car's engine, and the cap-like plant sections that cover vulnerable parts. One of the most famous hoods in literature is the red one worn by the main character in "Little Red Riding Hood."