That is a treaty.
When an agreement is formed between two nations the mort popular term is Treaty.
treaty
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A call option is an agreement between a buyer and a seller to settle on the price and production of a stock or product. If one party breaks the call options then the contract/agreement is null and void.
Most popular word is "treaty", for example NATO = North Atlantic Treaty Organisation. You can also look for Vienna Convention On The Law Of Treaties (from 1969) to find out more about such agreements.
An agreement between four parties is typically referred to as a "quadripartite agreement" or a "four-party agreement." This type of contract outlines the rights and obligations of each party involved and is used in various contexts, such as business deals, partnerships, or collaborative projects. Each party must agree to the terms for the agreement to be valid and enforceable.
treaty
You would call this agreement to meet someone or somewhere a "appointment".
To my knowledge and I am not an attorney, this would be an issue for a small claims court judge to decide if there is some dispute of payment involved in a contractual agreement between two parties. If in doubt call an attorney.
Price fixing (it is illegal).