Oh it's a interjection which can express a wide range of meanings, such as joy, wonder, amazement, irony, desire, among others.
In the phrase "ah, what a fright" the ah is a sound mark of the astonishment caused.
When saying "oh, but I wanted so much", the interjection reinforces the desire.
In "oh how beautiful!", the interjection means admiration, joy and even irony.
The meanings of the interjection ah can even be contradictory. Its meaning will depend on the context in which it is used, and on the words that join the ah to compose an expression.
The ah alone can come before a placement, as a way to get someone's attention. As in: "Oh, let me tell you something".
When something frustrating has been said, done, or shown, the answer can also be an isolated "ah".
With a more nasal pronunciation, like an "ah", the interjection is a sign of doubt, and is used after an unclear question, for example.
Ah is also an electrical charge unit symbol and means a ampere hour.
Examples of using Ah in expressions:
- Ah good - Okay, right.
- oh ok - ok, yes
- Oh no - Annoyance or frustration
- Oh yeah - You're right
- oh go - leave it
- Ah boy - Informal greeting when someone has done something admirable