Interjection, Definition and Examples

Oh! , Ah! , Ooh! , Alas! , Help! , Pooh! , When! , Look out! , Cheers! , Nice one! , Gosh! , Oh dear! , Look here! , Bless my soul! 
These are exclamations or emotional noises. As a part of speech, they are termed “Interjections”. Sometimes they are formed by actual words, sometimes not. We use them to express sudden feelings of joy, pain, surprise, disgust, anger, etc. They are generally marked by an exclamation mark or a question mark. They stand alone, as above; they may be loosely added on to a sentence.
Oh no – I can’t bear to watch any longer!
Dear me – what has happened to your clothes!
There now – don’t cry!
Many interjections or exclamatory statements are elliptical – that is, they refer to previous parts of a conversation or text with words left out or implied.
What an experience!
Poor fool lad!
Interjections may express:
Joy: as, Hurrah! Huzzah!
Grief: as, alas!
Surprise: as, Ha! What!
Approval: as, Bravo!
Certain groups of words are also used to express some sudden feelings or emotions, as:
Well done!
Good gracious!
For shame!
Ah me!