Agreement

An understanding between entities to follow a specific course of conduct.

"to enter an agreement;  the UK and US negotiators nearing agreement;  he nodded his agreement."

A state whereby several parties share a view or opinion; the state of not contradicting one another.

"The results of my experiment are in agreement with those of Michelson and with the law of General Relativity."

A legally binding contract enforceable in a court of law.

(grammar) Rules that exist in many languages that force some parts of a sentence to be used or inflected differently depending on certain attributes of other parts.