Claim

People assume the important part of a patent is the description of the invention. It is not. The important part is a numbered sentence near the end that most inventors never read carefully.

In simple words

A single, carefully worded sentence that defines the legal boundary of what the patent covers. Everything inside the words of a claim is protected; everything outside them is not.

Think of it as

The fence around your land. The description tells people what the land looks like; the claim says where the fence runs.

Why it matters

Infringement is decided by reading the claims. Validity is decided by reading the claims against the prior art. Two patents with identical descriptions and different claims are worth completely different amounts of money.

A simple example

“A container made of steel” is not infringed by an aluminium container. “A container made of metal” is - but it is also far more likely to be anticipated by an old metal container somewhere in the prior art. Every word is a trade between scope and survival.

Common mistake

Believing that adding more words makes a claim stronger. Every extra word is a further condition an infringer has to meet, so it usually makes the claim narrower and easier to design around.

Where it comes from

Patents Act 1970 - section 10(4)(c) and 10(5); scope of rights in section 48