What is the meaning of Oh?

Expression of surprise.

Expression of wonder, amazement, or awe.

Expression of understanding, affirmation, recognition, or realization.

A word to precede an offhand or annoyed remark.

A word to precede an added comment or afterthought.

An invocation or address (similar to the vocative in languages with noun declension), often with a term of endearment.

Exclamation for drama or emphasis (often poetic).

Expression of pain. See ouch.

Space filler or extra syllable, especially in (popular) music.

Expression of mild scepticism.

A word to mark a spoken phrase as imaginary.

An utterance of oh; a spoken expression of surprise, acknowledgement, etc.

To utter the interjection oh; to express surprise, etc.

The name of the Latin-script letter O/o.

the digit 0 (especially in representations of speech)

oh (expression of surprise, etc.)

younger sibling

Expression of surprise: oh!

A letter of the Juǀ'hoan alphabet, written in the Latin script.

and

milk

oh (expression of surprise, etc.)

oh

Abbreviation of olohuone (living room).

oh

oh (expression of surprise, etc.)

oh

oh!

oh! ah!

Alternative form of ó

Alternative form of of

oh (expression of awe, surprise, pain or realization)

Alternative spelling of o

Alternative spelling of o

Source: wiktionary.org