Wah is an exclamation that usually expresses positive opinion. It depends on the tone of the story whether you can translate it as simple "wow!" or use some other expression. Hope this helps.

this is a term for appreciation of some deed, job, creation, action or gesture

Wah is Bravo

As none of the answers posted yet give a full explanation of the term, I am posting a separate answer, with apologies to the other posters. Petrapot has made the most important point, that it is the tone in which the word is uttered that really determines its meaning. Having said that, it can convey a variety of meanings. So the context is important in determining its exact meaning. Some of the ways in which it is used is given below.

The most common usage is to provide instant appreciation to some clever poetry or deed. Situations could be a poet recites a line of poetry, and the listeners if they approve of it respond with “Wah”, or “Wah, wah”. Again the tone here can indicate the level of approval. It could be a rave, total approval, in which case the utterance of the word may be accompanied by slapping of thighs, or a very grudging approval, in which case the word is uttered slowly and in low volume, no repetitions or slapping of thighs, too. Here it is almost like giving the poet the benefit of doubt, where he is expected to redeem himself in the next lines he recites.

Another usage is the questioning one, where “wah” is used to refute politely some statement, for example,

Wah janab, aap to gazab karte hai.

Here the word is not expressing any appreciation, on the contrary it is mildly questioning or expressing mild disapproval of some action.

Another interesting usage is when it comes along with “Are” as in “Are wah”. This is used when one doesn't expect someone to do something, but the person manages to do it.

Are wah! Yah to tumne bahut achchha kar diya.

Wah can also be used to raise a complaint. In this case it is used along with “re” as in,

Wah re, kismet! Kya is garib ko yah dekhna bhi baaki tha?

In this usage it more like “Alas” in meaning.

Many other possibilities are also there, which a good Hindi or Urdu dictionary will clarify.