Patent, Copyright, Trademark, and Trade Secrets

Intellectual Property is a broad class of property, similar to 'real estate' (land), and 'chattels' (movable physical goods).
Intellectual property generally includes four very different kinds of rights: Patent, Copyright, Trademark, and trade secrets. Traditionally, trade secret law is found within the unfair competition heading. Patents, and copyrights are regulated by the U.S. Congress, through the U.S. PTO (Patent and Trademark Office). Trademarks are regulated both by the U.S. Congress and by State laws. Trade secrets are primarily regulated at the State level.

Trade Secrets are private information held by a business, that are not generally available to the public, and which have commercial value to the business.
Because of its secret nature, a trade secret is not a Patent, a copyright, or a trademark.
Abuse of trade secrets is considered a form of unfair competition, even though the abuse may not be obvious competition.
Trade secrets are primarily protected under State law, including considerable "Common Law" interpretations. Particular factors vary widely from State to State.
Examples:
Customer lists, and lists of particular contacts at customers' locations, are very common trade secrets.
Particular manufacturing details that are not publicly available can be protectable trade secrets.