Agreement in principle:
Defintion: In law, an agreement in principle is a stepping stone to a contract. Such agreements with regard to the principle are usually considered fair and equitable. Even if not all details are known, an agreement in principle may, for example, outline a schedule of royalties.
http://en.wikipedia.org/wiki/Agreement_in_principle
Defintion: An agreement in principle is an agreement that makes the major terms clear, laying the groundwork to make a contract. Agreements in principle are not legally enforceable as a general rule because they are not formal contracts, although sometimes they will be used in legal cases if there is a dispute.
http://www.wisegeek.com/in-law-what-is-an-agreement-in-princ...
Definiton:
agreement in principle n (accept an idea in theory, though not in fact) - a fi de acord în principiu loc.vb.
http://www.wordreference.com/enro/agreement in principle