35 USC 112, 2^nd paragraph (definiteness requirement) – “The specification shall conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the applicant regards as his invention.”

There are two separate requirements set out by the second paragraph of §112, 2^nd paragraph: 1) The claims must set forth the subject matter the applicants regard as their inventions; and 2) The claims must particularly point out and distinctly define the metes and bounds of the subject matter that will be protected by the patent (often called the definiteness requirement). The USPTO will consider A-E to determine whether the claims do or don’t meet the §112, 2^nd paragraph requirements.

A. Claim Terminology:

• Applicants can use whatever terms they chose for defining their invention in the claims, so long as those terms are not used in ways contrary to accepted meanings in the art. (“Oval” cannot be defined as trapezoidal.).
• The use of relative terms in claims is a factual and subjective test, not an objective test. Terms that are scrutinized by the PTO include about, essentially, similar, substantially, type, and relatively.” These, and similar, terms should be defined in the specification as tho their exact meaning relative to the invention.
•  Trademarks or trade names - Trademarks or trade names identify the source of goods, not the goods themselves. While trademarks can be used in the claim language [MPEP 608.01(v)], the claim is indefinite 1) if they are used in a limitation intended as a description of a material or 2) their use cases confusion as to the scope of the claims.
• Markush Groups – A Markush group which is a way of limiting claim to the members of the group of individual elements (e.g., members “selected from the group consisting of A, B and C”) is definite. [A Markush group is a way of limiting a group to a set of individual elements. A markush group is used when a genus can be defined as a group that consists of particular individuals. It's a special/alternate way of expression that selects from a group "consisting of A, B and C" (closed-ended transition phrase). This wording is used (for among other reasons) to identify elements with a common trait, and the exact language must be used.]
• Omnibus claims – Omnibus claims which read “a device substantially as shown and describes” are indefinite. These claims are not allowed in the US because they do not express the metes and bounds of the claim.
• The claims should be as self-contained as possible and should not reference tables and figures unless necessary.

B. Consistency with Specification or Prior Art: Claims that are inconsistent with their supporting specification or the prior art cannot be considered reasonably particular and distinct, even though the terms of the claims may seem definite. [MPEP §2173.03]

Claims should be self-contained, when possible. In circumstances where an invention cannot be defined in words and it is more concise to incorporate figures or tables by reference, it is acceptable to do so.

C. Breadth of Scope: The scope of the claims must be defined clearly under section 112, 2^nd paragraph. (It is not the breadth of the scope, but whether that scope is clearly defined that matters to a sections112, 1^st paragraph issue.) An example of indefinite claim based on lack of scope includes: “between 58% and 75% of the height of the rider” when the rider’s height is undefined.

Stating specific numerical ranges in a claim does not usually raise an issue of definiteness. Exceptions include 1) narrow and broader ranges in the same claim (e.g., a length between 5 and 16 inches, preferably between 7 and 8 inches) and 2) open ended numerical ranges (e.g., at least 12%) which should be checked carefully for consistency with examples and guidelines in the rest of the disclosure. In order to avoid a §112, 2^nd paragraph rejection, keep exemplary language (specific examples) and preferences out of the claim language and limit them to the specifications.

D. Lack of Antecedent Basis: References in a claim to, for example, “said lever” or “the lever” when there is no previous reference in the claim to a lever creates uncertainty as to what the claim is referring to. A lack of antecedent basis results in indefiniteness, unless the scope of the claim could be reasonably ascertained by a skilled artisan.

E. Product and Process: A product-by process claim is a product claim defining the product in terms of the process that makes it. Such a claim is not inherently indefinite. However, a product and process claim in which both an apparatus and the process for using it are claimed is indefinite.

Claims to a process that do not include any steps to be taken in carrying out the process are usually held to be indefinite. For example, a claim to “a process for using X of claim 4 to isolate and purify Y” was found indefinite because it recites a use without givig steps for how the use is practiced.