A more thorough explanation:

Definition: Undue-breadth rejection is a finding by a patent examiner that a patent claim is too broad and seeks a patent monopoly on more than the invention. This means that the claim is not specific enough and includes other possible ways of accomplishing a function. For example, a chemical claim is more likely to be rejected for undue breadth than a claim on a machine because future discoveries are less predictable.

Examples:

• A patent application claims a chemical compound that can be used as a pesticide. The examiner finds that the claim is too broad because it covers all possible variations of the compound, including those that have not been discovered yet. This is an example of undue-breadth rejection.
• Another patent application claims a machine that can perform a specific function. The examiner finds that the claim is specific enough and does not seek a patent monopoly on more than the invention. This claim would not be rejected for undue breadth.

The examples illustrate how undue-breadth rejection can occur when a patent claim is too broad and seeks to cover more than the invention. This can happen when the claim is not specific enough and includes other possible variations or ways of accomplishing a function. Patent examiners look for specific and clear claims that do not seek to monopolize more than the invention.