A more thorough explanation:

A fingerprint claim is a type of patent claim that differentiates a material from prior art based on some physical feature, such as melting point or spectrum, rather than its chemical composition. This type of claim is allowed only when the chemical composition cannot be determined or cannot be distinguished from prior art.

For example, a company may file a patent for a new type of plastic that has a unique melting point. The patent claim would describe the plastic as having a specific melting point, which distinguishes it from other plastics in the market. This type of claim is useful when the chemical composition of the plastic is similar to other plastics, but the unique melting point makes it a novel invention.

Another example of a fingerprint claim is a patent for a new type of metal alloy that has a unique spectrum. The patent claim would describe the metal alloy as having a specific spectrum, which distinguishes it from other metal alloys in the market. This type of claim is useful when the chemical composition of the metal alloy is similar to other metal alloys, but the unique spectrum makes it a novel invention.