The general rule is that the contract is king. Arnold v Britton concerned the service charge provisions in 25 holiday chalet leases.Do not define a term unless you use it in the agreement. I have seen agreements with many definitions which aren't used anywhere in the body of an agreement. Written proof is not needed. Definition of a Contract. A contract is created at law when there is a mutual exchange of promises upon reasonably understandable terms and conditions. 'Hereinafter' is an adverb, a word that modifies the verb, an action, in a sentence. 'Hereinafter' means 'in the following part' of a legal document. A legally valid and binding contract requires a consideration.