Hurrah! we have a holiday! Alas! How did it happen? Hush! The baby is asleep.
In the above sentences we notice that the words hurrah, alas and hush have no grammatical connection with the sentences in which they occur. The meaning of these words is very plain. They call our attention very closely to what follows, and indicate that the speaker in each case is very much in earnest.
Such words as hurrah, alas, and hush, are called interjections.
An interjection is a word used to express strong feeling, and is not grammatically connected with any other word in a sentence.
The most common interjections are: ah alas bah bravo good good-by ha hark hello hush hurrah indeed look oh pshaw see tut welcome what