A handshake is often used to mean there is an agreemnet
When pepole feel or think the same way about somtehing, they agree. Someitmes it is improtant to write down or make a pormise to what has been agreed on. This is claled an agreeemnt. Agreemetns are comomn in law and bsuiness. For examlpe, when a perosn takes out a loan or hires soemone to work, an agreement is usually sigend so everoyne undesrtands what must be done and in what time it must be done.