Ab initio: (Latin) from the beginning.

Abatement: Reduction or rebate of an amount owed, usually by agreement with the person to whom the debt is owed. Debts or claims may be abated pro rata if there is not enough money to meet them all.

Acceptance: One of three requirements for a valid contract under common law (the other two being offer and consideration). A contract does not become legally binding until one party has made an offer and the other party indicates his readiness to accept the terms of the offer. Acceptance must be unconditionally communicated to the offeror while the offer is still open. Acceptance of an offer can, in certain circumstances, be implied by conduct.

Accord and Satisfaction: A contract may be discharged if one party, who has complied with his part of the contract, accepts compensation from the other party instead of enforcing the contract. The accord is the agreement by which the obligation is discharged. The satisfaction is the consideration (usually money and of a lesser value) which makes the agreement operative.

Acquiescence: Action or inaction which legally binds someone, even unintentionally. For example, an action such as accepting goods from a supplier will be binding if it implies recognition of the terms of a contract.

Act of God: An event resulting from natural causes, without human intervention (such as floods or earthquakes). Insurance policies often exclude acts of God.