Русско-англо-русский юридический словарь

Two parties purport to "agree" to have concluded a contract for a car, but have not actually worked out a price, it cannot be said that they have concluded a contract. The price would seem to be an "essential term". If further, the "buyer" had gone to a car dealer and said he would pay £10,000 for a car, but has not said which car, a "essential term" is probably lacking again. The price and the thing exchanged are examples of essential terms in simple sale of goods contracts. (Wikipedia)

essential term (of a contract) – a provision required for a contract to exist. The client must give informed consent in writing to both the essential terms of the transaction and the lawyer's role in it. (translegal.com)

Nevertheless, LOI’s can provide confirmation to parties that they have reached consensus on the essential terms of a transaction before spending time, effort, and money drafting an enforceable agreement. (Letter of Intent of Contract? Tips to Avoid a Costly Mistake by Brian Moore, Saalfeld Griggs PC)

An offer is a proposal to enter into an agreement and must express the intent of the person making the offer to form a contract, must contain the essential terms -- including the price and subject matter of the contract -- and must be communicated by the person making the offer. A legally valid acceptance of the offer will create a binding contract. (Nolo's Plain-English Law Dictionary)