What is the “plain meaning” of a claim term?

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.

The “plain meaning” of a claim term refers to the ordinary and customary meaning given to the term by those of ordinary skill in the art at the relevant time. As stated in the MPEP, “[T]he ordinary and customary meaning of a claim term is the meaning that the term would have to a person of ordinary skill in the art in question at the time of the invention, i.e., as of the effective filing date of the patent application.” (MPEP 2111.01)

This meaning can be evidenced by various sources, including the words of the claims themselves, the specification, drawings, and prior art. However, the specification is generally considered the best source for determining the meaning of a claim term.