Interjections
Interjections are words used to express strong feeling or sudden emotion. They are included in a sentence - usually at the start - to express a sentiment such as surprise, disgust, joy, excitement or enthusiasm.
An interjection is not grammatically related to any other part of the sentence.
Examples:
Hey! Get off that floor!
Oh, that is a surprise.
Good! Now we can move on.
Jeepers, that was close.
Yes and No
Introductory expressions such as yes, no, indeed and well are also classed as interjections.
Examples:
Indeed, this is not the first time the stand has collapsed.
Yes, I do intend to cover the bet.
I'm sure I don't know half the people who come to my house. Indeed, for all I hear, I shouldn't like to. (Oscar Wilde)
Well, it's 1 a.m. Better go home and spend some quality time with the kids. (Homer Simpson)
Phew!
Some interjections are sounds.
Examples:
Phew! I am not trying that again.
Humph! I knew that last week.
Mmmm, my compliments to the chef.
Ah! Don't say you agree with me. When people agree with me,I always feel that I must be wrong. (Oscar Wilde)
Read more at http://www.grammar-monster.com/lessons/interjections.htm#Ktb5TgQJLZlTkCII.99