Русско-англо-русский юридический словарь

An oral contract is a contract, the terms of which have been agreed by spoken communication. This is in contrast to a written contract, where the contract is a written document. There may be written, or other physical evidence, of an oral contract – for example where the parties write down what they have agreed – but the contract itself is not a written one. (Wikipedia)

With this in mind, oral contracts should be reserved for simple agreements – the simpler the contract, the less chance that both parties will find themselves in court disputing the unspecified details of a verbal arrangement. (360 Business Law)