Pronounced "VAH-lay", this Spanish
exclamation is one of the most common words one hears in Castillian/Castilian Spanish
conversation. It is roughly equivalent to the English "OK
", but has more general uses.
Typical uses of vale include solicitation of acknowledgement, (as in, Doble a la izquierda, ¿vale? -- Turn to the left, OK?); acknowledgement that you have heard and intend to comply with an instruction, (as in, Vale; izquierda -- OK, left, got it); as a less-than-fully-polite-but-not-rude greeting; and even sometimes to simply indicate that you are ready to hear whatever it is someone wants to say, (as if to say, "What do you want?").
One way that OK and vale are not synonymous is in the phrase "It's OK, don't worry about it", or "I'm OK". You would not use the word vale in this case, but instead, the phrase, No pasa nada, which literally means, "Nothing happens", but is roughly the same thing as, "It's OK."
It is worth noting that the word "OK" is also used in Spanish -- both in European Spanish and New-World Spanish. The difference is that while Spanish in the Americas uses "OK" the same way we do in English (and does not employ vale), Spanish in Spain uses "OK" in a different way.*
A Spaniard would say OK instead of vale when (s)he wants to express emphatic agreement or encouragement to the other person. So, in Spain, OK is roughly equivalent to the English, "Exactly!".
*The comments on Spaniards´ use of OK are based on my experience in Andalucia. While I am quite certain that vale is used all over Spain, it is possible that my description of the application of OK is unique to Andalucia.