Just this one word needs a massive amount of info so please check main menu for What is Contract? section.

However these snippets are amongst the best known meanings.

 

Treitel

‘A contract is an agreement giving rise to obligations which are enforced or recognised by law. The factor which distinguishes contractual from other legal obligations is that they are based on the agreement of the contracting parties.’

Pollock

‘A promise or set of promises which the law will enforce.’

Anson

‘The law of contract may be provisionally described as that branch of the law which determines the circumstances in which a promise shall be legally binding on the person making it.’