Related: agree, bind together, charter, constrict, private law

A contract is an legal agreement such as a license, lease, agreement, treaty.

/*Contract \Con"tract\, n. [L. contractus, fr. contrahere: cf. F.
   contrat, formerly also contract.]

   1. (Law) The agreement of two or more persons, upon a
      sufficient consideration or cause, to do, or to abstain
      from doing, some act; an agreement in which a party
      undertakes to do, or not to do, a particular thing; a
      formal bargain; a compact; an interchange of legal rights.
      --Wharton.*/

The GNU General Public Law is a contract between two or more persons.