An interjection is a word used in a sentence to express some feeling of the mind. As a matter of face, an Interjection is not a part of the construction of a sentence. So, we can say that parts of speech except Interjection have some grammatical link with some other word in the sentence in which they are found.
Many people think that as the word ‘Interjection’ that we use for such situations is not a part of speech, it should be given no word at all. But we must give it a name, and however, because it is a word and grammar takes care of every word that is present in human speech. We always put an exclamation mark after an Interjection. Here are some examples of interjections.

           Joy                                          Hurrah, Huzza, aha, alack,
            Grief                                       oh, ah, alas,
            Amusement                            ha, ha,
            Approval                                Bravo,
            Weariness                              Heigh-ho,
            Attention                                Lo, bark, hush, hist
            Reproof                                  Fie, Fie,
            Contempt                               Stuff, bosh, tut-tut, pooh,
            To call someone doubt          Ho, holloa, hum, hem, humph,