English101

Interjections
Hi! That's an interjection. :-)
Interjection is a big name for a little word. Interjections are short exclamations like Oh!, Um! or Ah! They have no real grammatical value but we use them quite often, usually more in speaking than in writing. When interjections are inserted into a sentence, they have no grammatical connection to the sentence. An interjection is sometimes followed by an exclamation mark (!) when written.
Interjections like er and um are also known as "hesitation devices". They are extremely common in English. People use them when they don't know what to say, or to indicate that they are thinking about what to say. You should learn to recognize them when you hear them and realize that they have no real meaning.
The table below shows some interjections with examples.
interjection meaning example

ah          expressing pleasure                     "Ah, that feels good."
              expressing realization                  "Ah, now I understand."
              expressing resignation                "Ah well, it can't be heped."
              expressing surprise                     "Ah! I've won!"


alas       expressing grief or pity                "Alas, she's dead now."


dear      expressing pity                            "Oh dear! Does it hurt?"
             expressing surprise                    "Dear me! That's a surprise!"


eh          asking for repetition                     "It's hot today." "Eh?" "I said it's hot today."
             expressing enquiry                       "What do you think of that, eh?"
             expressing surprise                       "Eh! Really?"
             inviting agreement                       "Let's go, eh?"


er          expressing hesitation                      "Lima is the capital of...er...Peru."


hello,     expressing greeting                        "Hello John. How are you today?"
hullo      expressing surprise                        "Hello! My car's gone!"


hey        calling attention                             "Hey! look at that!"
             expressing surprise,joy                  "Hey! What a good idea!"


hi           expressing greeting                       "Hi! What's new?"


hmm      expressing hesitation,                    "Hmm. I'm not so sure."doubt
             or disagreement


oh, o     expressing surprise                        "Oh! You're here!"
             expressing pain                             "Oh! I've got a toothache."
             expressing pleading                       "Oh, please say 'yes'!"


ouch      expressing pain                             "Ouch! That hurts!"


uh          expressing hesitation                     "Uh...I don't know the answer to that."


uh-         expressing agreement                   "Shall we go?" "Uh-huh."
huh

um,         expressing hesitation                    "85 divided by 5 is...um...17."
umm

well        expressing surprise                       "Well I never!"
              introducing a remark                    "Well, what did he say?"