A trademark is basically a brand name. A trademark is a word, phrase, symbol, design (or combination of words, phrases, symbols or designs) that identifies and distinguishes the source of the goods (or services) of one party from those of others. Common trademarks include Ford for cars, McDonalds for hamburgers, and Kodak for cameras. An example of a symbol is the apple with a missing piece for Apple Computers.
Trademark rights are acquired by using the mark in association with the sale of goods or services. There is no requirement that a mark be registered, but there are a number of benefits to registering a mark, including a notice to the public of the registrant's claim of ownership of the mark, a legal presumption of nationwide ownership, and the exclusive right to use the mark on or in connection with the goods or services set forth in the registration.
To obtain a federal registration the mark must be used in interstate commerce, or in commercial activities in more than one state. If the mark is only used in a single state it is possible to obtain a state registration, or to claim common law trademark rights.
For more information on trademarks, go to the Patent Office Web site, www.uspto.gov. The most informative basic page can be found here: Trademark Basics.