In a patent or patent application, the claims define in technical terms the extent, i.e. the scope, of the protection conferred by a patent, or the protection sought in a patent application. In other words, the purpose of the claims is to define which subject-matter is protected by the patent (or sought to be protected by the patent application). This is termed as the "notice function" of a patent claim—to warn others of what they must not do if they are to avoid infringement liability.[1][2][3] The claims are of paramount importance in both prosecution and litigation.[4]
For instance, a claim could read:
"An apparatus for catching mice, said apparatus comprising a base, a spring member coupled to the base, and ..."
"A chemical composition for cleaning windows, said composition substantially consisting of 10–15% ammonia, ..."
"Method for computing future life expectancies, said method comprising gathering data including X, Y, Z, analyzing the data, comparing the analyzed data results..."
^See, e.g., PSC Computer Prods., Inc. v. Foxconn Int’l, Inc., 355 F.3d 1353, 1358 (Fed. Cir. 2004) ("One important purpose of the written description is to provide notice to the public as to the subject matter of the patent, while the claim provides notice as to the scope of the invention."). See also Nautilus, Inc. v. Biosig Instruments, Inc., 572 U.S. __, 134 S. Ct. 2120 (2014) ("To tolerate imprecision just short of that rendering a claim 'insolubly ambiguous' would diminish the definiteness requirement's public-notice function and foster the innovation-discouraging 'zone of uncertainty' [citation omitted] against which this Court has warned."); McClain v. Ortmayer, 141 U.S. 419, 424 (1891) (a patent claim must be precise and clear enough to give the public clear notice of what is claimed, thereby "appris[ing] the public of what is still open to them").