How is the term “substantially” interpreted in patent claims?

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 term “substantially” in patent claims is often used to describe a particular characteristic of the claimed invention. According to MPEP 2173.05(b), it is considered a broad term. The interpretation depends on the context and the guidance provided in the specification. For example, in In re Nehrenberg, the limitation “to substantially increase the efficiency of the compound as a copper extractant” was found definite based on the general guidelines in the specification. Similarly, in Andrew Corp. v. Gabriel Electronics, the court held that “substantially equal E and H plane illumination patterns” was definite because one of ordinary skill in the art would understand its meaning.