How to define a custom term in a patent claim?

I want to define a custom term in my claim and the term will be used in later parts of the claim. For example,

A method of an electronic device, comprising:

running by the said device, an application wherein the application checks stability;


Here, the term "stability" is a custom term which has a definition like "XYZ". Now how can I define the term within the claim? What should be the structure of the sentense?

  • 2
    A good question. I think you define such terms in the specification, but would prefer to defer to someone more qualified to answer.
    – Eric S
    Oct 7, 2021 at 21:10
  • 2
    Writing a good patent application is possible for a pro se inventor but unlikely. If you are going to do this yourself it will take a lot of study.
    – George White
    Oct 7, 2021 at 21:34

2 Answers 2


Most if not all patent laws across Europe, including the European Patent Convention, require the claimed subject-matter to be clear without resorting to any other part of the patent specification. This can be said more nicely as "the claims must be clear in themselves when read by the skilled person (not including knowledge derived from the description);"

This means that you must include any definition necessary to understand the claimed subject-matter, be it the definition of a term, the definition of a parameter, and/or the definition of a method for measuring a parameter. You can find some more information in the Guidelines for Examination.

The definition of the term within the claim can be in any form as long as it can be clearly understood. Sometimes it is easier not to use the term that is to be defined in the first place and directly type in its meaning.


You do not usually define terms in a claim but in the specification. Patent applicants are allowed to redefine words and give them special meanings. You need to do it thoughtfully because if you pin down a definition too strongly you may be inadvertently narrowing the claim.

  • Thanks for your answer. I understand the weakness of redefining a term. Accepting the weakness, is there any way to do it in the claim? Can multiple wherein clause be used in a single sentence (i.e. "running by the said device, an application wherein the application checks stability wherein the stability means XYZ;" ) ? Oct 8, 2021 at 1:40
  • Yes that can work. Redefining a term is fine but can be tricky
    – George White
    Oct 8, 2021 at 1:58

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