Under common law and the U.S. Lanham Act, a trademark is "any word, name, symbol, or device or any combination thereof adopted and used by a manufacturer or merchant to identify his goods and distinguish them from those manufactured or sold by others."

Trademarks originate from the rule that no one has the right to sell products that belong to another person or company.
The SlideShow below discusses trademark issues in more detail.

A direct contribution of EP to trademark law concerns domain name infringements.
A domain name is a company's logical address or source identifier on the Internet. The holder of a domain name may be entitled to protection by the U.S. Patent and Trademark Office (PTO) if the domain name also functions as a trademark or service mark.

The Patent and Trademark Office (PTO) may deny federal registration of a domain name if the mark is likely to be confused with a previously registered trademark or service mark. The test for confusion is based on the likelihood with which an average consumer in a similar marketplace would confuse the source of the product or services given similarities in sound, appearance, meaning, or connotation of the two marks.

Domain name registration is done on a first-come, first-served basis without examining whether the proposed name would violate anyone else's proprietary rights. The problem with the first-to-file approach arises when the domain name will also function as a trademark or service mark. If a domain name is challenged by another individual or organization as an infringement under trademark or service mark law, the registration service will place the domain name "on hold" to make it unusable by anyone until the matter is resolved.
The next lesson will cover patents and patent issues.