What, exactly, are trade secrets?

Trade secrets vary in their definition from state to state, so there is no single definition. But in general, a trade secret can be anything you know that (A) provides a business advantage, (B) is not generally known in the industry, and (C) for which you have taken reasonable steps to keep secret. In most states, the trade secret need not be particularly inventive or novel, so long as it is not generally known in the industry. A famous example is the method for making Coca-Cola. Something cannot be a trade secret when it is impossible to keep secret, such as what the parts of a product that you distribute to the public, since anyone can take the product apart and find out the secret.