What is a dehydration reaction with respect to alcohols?
Well, in a dehydration reaction, the elements of water are spat out from the reactive molecule...........
And typically, we take an alcohol, treat it with acid (to protonate the oxygen), and make it a better leaving group, give it a good blast of heat, and we get the olefin and water as products.
Phosphoric acid is typically used for these reactions. All of this will be explained much better in your organic chemistry text.