Can an applicant be their own lexicographer?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

Yes, an applicant can act as their own lexicographer. The MPEP states, “An applicant is entitled to be their own lexicographer and may rebut the presumption that claim terms are to be given their ordinary and customary meaning by clearly setting forth a definition of the term that is different from its ordinary and customary meaning(s) in the specification at the relevant time.” (MPEP 2111.01)

However, it’s important to note that any special meaning assigned to a term must be clearly defined in the specification. The definition must be sufficiently clear that any departure from common usage would be understood by a person experienced in the field of the invention.