In very simple terms, elimination recations are tose which follows the mechanism of removal of a part of the recating compounds to form products. This can take place either in a single step, also called E1 mechanism; and it can also take place in two steps, when it is called as E2 mechanism.

Example, eleimination reactions undergone by 2-bromopropane. 

CH₃CH-BrCH₃ + NaOH → CH₂=CHCH₃ + NaBr + H₂O

This s an example of E2 mechanism. In the first step, 1 H and Br is remobed from CH₃CH-BrCH₃ to give CH₂=CHCH₃. In the second step NaOH dissociates and Br produced in the first step combines with Na to give NaBr and simultaneously H₂O is released.