Very aromatic, with a deep earthiness, white truffle oil is olive oil infused with the flavor and aroma of white truffles. It's used as a finishing touch (heat can alter its flavor) and usually drizzled on just before serving. Most commercial truffle oils are made by mixing grapeseed oil or light olive oil with one or more chemical compounds like 2,4-dithiapentane, which is the most prominent of the hundreds of aromatic molecules contained within white truffles. Some versions contain little or no actual truffle. Truffle oil is also made with black truffles from France.
Truffle butter and truffle salt can also give a dish truffle flavor at an affordable price.
Quality varies wildly. Ask for a recommendation (even better, a taste) at your favorite Italian market or specialty food store.
Keep truffle oil refrigerated for longer storage.