A patent grants an exclusive right to an invention, which requires that the patent applicant particularly define the subject matter what he/she wishes to protect in the given patent application. It is the claims in a patent which defines the scope of the exclusive right granted in that particular patent.
35 U.S.C. § 112 states that the specification of a patent document shall conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the applicant regards as his invention. One of the fundamental rule of the patent application is that the applicant “shall also particularly specify and point out the part, improvement, or combination which he claims as his own invention or discovery.” In other words, the statute of the claims presents two main requirements, that is, first set forth the subject matter; and then particularly point out and distinctly claim it. That is, the first requirement provides that the subject matter shall be selected, and the second requirement provides that boundary of protection sought must be defined.
35 U.S.C. § 112(b) requires that a claim not be indefinite, since an indefinite claim might not be easily understood by a person skilled in the related art to which the invention pertains. Some of the past case laws provide that a claim can be indefinite if it is “insolubly ambiguous, and no narrowing construction can properly be adopted,” but there is no clarity in this aspect and shall be taken with a pinch of salt. Therefore, it is required that the claims clearly define “the invention,” such that a person skilled in the art, e.g. the patent examiner and judges may later be able to construe the claims can understand what the boundaries of the invention i.e. what is covered and what is not, as for the particular patent is concerned.
It is to be noted that the pertinent sections of the law only point out that a claim is necessary, but does not define what a claim format or structure shall be. Such information may be obtained by referring to various patent rules as provided by the USPTO, or can be construed from various judgements in the domain.