Claims

define the invention and are what aspects are legally enforceable. The specification must conclude with a claim particularly pointing out and distinctly claiming the subject matter which the applicant regards as his invention or discovery. The claim or claims must conform to the invention as set forth in the remainder of the specification and the terms and phrases used in the claims must find clear support or antecedent basis in the description so that the meaning of the terms in the claims may be ascertainable (clearly understood ) by reference to the description. (See 37 CFR § 1.58(a)).

-- see MPEP 608.01(i) for more

Context: Patent 

The claims define the matter for which protection is sought. They must be clear and concise and fully supported by the description.
  

The part of a patent document which defines, in legal terms, the subject matter which the applicant regards as his invention and for which protection (and monopoly) is sought or granted. Each claim is a single sentence in a legalistic form that defines an invention and its unique technical features. Claims must be clear and concise and fully supported by the description.

Most patent documents, including international applications, must contain at least one claim. Claims are usually located at the end of a patent document, after the detailed description, and before any drawings or Search Report. In electronic patent documents such as international applications (in PDF format) on the PATENTSCOPE® Search Service, claims are easily located by clicking the "Claims" bookmark.