Dehydration of a secondary alcohol occurs readily in the presence of a strong acid and proceeds via an e1 mechanism. what does e1 stand for?

E1 stands for a Unimolecular Elimination.

E1 reaction results in the formation of a double bond. This is unimplecular reaction because rate determining slow step is the dissociation of the leaving group and formation of carbocation.

There is two steps in E1 mechanism:

1) group leaves to form a carbocation intermediate.

2) base deprotonates a beta carbon to form π bond.