Why is dehydrohalogenation reaction in haloalkane termed as `beta-elimination ?

What do you mean by dehydrohalogenation reaction ?

Explain the following : Dehydrohalogenation reaction.

Why are haloarenes more stable than haloalkanes ?

Most important chemical reactions of haloalkanes are their substitution reactions. Arrange the four isomeric bromobutanes in the increasing order of their reactivity towards S_N1 reaction.

Haloarenes are less reactive towards nucleophilic substitution reactions than haloalkanes. Give a reason.