Interjection
Interjection is a word or a sound which expresses some sudden feeling of joy, sorrow, wonder, fear etc. For example:
Hurrah! We have won the match.
Alas! He has died.
Ah! What a dark night.
Bravo! You have completed the task in time.
Hush! Don't make a noise.
Some group of words are also used as interjections.
Ah me! For shame! Good heavens! Well done!