Quick answer
vale
Natural: OK / fine / got it
Literal: “it is worth”
How it is used
Vale.OK.
¿Vale?OK? — checking you agree.
Vale, vale.Alright, alright.
Nos vemos a las ocho, ¿vale?See you at eight, OK?
Where it is said
Spain above all. In Latin America: bueno, dale (Argentina), órale (Mexico).
A mini dialogue
— Te llamo luego.— I’ll call you later.
— Vale, hasta luego.— OK, see you.
Watch out
vale
Using vale in Latin America. It is understood, but it marks you instantly as someone who learned Spanish in Spain.
Check yourself
Which is the Spain-flavoured “OK”?