An interjection is a part of speech that usually has no grammatical connection with the rest of the sentence and simply expresses emotion on the part of the speaker, although most interjections have clear definitions. Filled pauses such as uh, er, um, are also considered interjections. Interjections are generally uninflected function words and have sometimes been seen as sentence-words, because they can replace or be replaced by a whole sentence (they are holophrastic). Sometimes, however, interjections combine with other words to form sentences, but not with finite verbs. When an exclamation point is not needed, a comma can take the place.
Interjections are used when the speaker encounters events that cause these emotions — unexpectedly, painfully, surprisingly, or in many other sudden ways. However, several languages have interjections that cannot be related to emotions.
The word “interjection” literally means “thrown in between” from the Latin inter (“between”) and iacere (“throw”).
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.
Some examples of interjections are:
Ouch, you stepped on my toe!
Oh no, I forgot that the exam was today.
Wow! That is a giant pumpkin!
Yippee! We won!
Whoa! Hold your horses!
Bravo, you did a great job!
Hey! Put that down!
The most common interjections which usually use in English examinations are:
oh, alas, ouch, Godspeed, we aye, aww, hey, yoo-hoo, Yuk
oh dear, Oh!, Gee!, Good grief, okey dokey, Ouch, ugh, wow
eureka., Uh, ouch, scat, Rah, Yay, Yikes, Ugh, come on, Ow
oops, Wow, Hurrah, Yippee, Shh, Mmm, ay, Tut-tut., aye man
long time no see, my foot, Aha, aye, Woe
Source : Wikipedia