A trademark search is an investigation usually conducted by the party that intends to register and use a new trademark. The purpose of the investigation is to establish if there are any existing trademarks already registered or in use by its trademark owners that may be similar to the new trademark or used on related products or for related services. If there are, the use and registration of the new trademark may be rejected to avoid the likelihood of confusion.
Therefore, it is advisable to conduct a trademark search before using or trying to register a new trademark to reduce the possibility of inadvertently infringing a third party’s intellectual property rights.
The United States Patent and Trademarks Office has a tool available here to conduct a preliminary search in their trademark database. However, it might be advisable to conduct a thorough trademark search with the assistance of a professional search firm because some parties may have "common law" trademark rights as a result of being the first to use a trademark in commerce (even if such a trademark is not registered at the federal or state level).
[Last updated in October of 2021 by the Wex Definitions Team]