Interjection

Interjections there the word which expresse sudden feelings and emotions of heart such as joy, grief, wonder, fear, anger, surprise, approval and disgust etc.

List of Common Interjections
 
O!, Oh!,  Ooh!,  Aye!,  Hello!,  Well!,  Ha!,  Ho!,  Hurrah!,  Ah!,  Alas!,  Hush! etc.
     
 
There are certain groups of words that are also used as Interjections

Examples
 Ah me!,   Dear me!,  Good heavens!  Good gracious!  Well done!  For shame!  etc.

Note: An Interjection is mostly followed by an exclamatory mark (!).

Examples
   
Hello! What are you doing there?

Hurrah! We have won the match.

Oh! I got such a fright.