Elasticity measures the extent of the response to a change in something. i.e. an elastic band can stretch to give more response. Personally I have an elastic demand function as when I go shopping, if something has been reduced I will buy more of it, whereas someone who has an inelastic demand function will be a lot less affected by changes in price. Try looking all the elasticity equations together and you will see that they are all really similar - it's quite easy once you've cracked it so don't worry.
