Real Dictionary

whether
conjunction: You use whether when you are talking about a choice or doubt between two or more alternatives.

whether in American English
if it be the case or fact that
conjunction: (used to introduce the first of two or more alternatives, and sometimes repeated before the second or later alternative, usually with the correlative or)

whether in British English
conjunction: used to introduce an indirect question or a clause after a verb expressing or implying doubt or choice in order to indicate two or more alternatives, the second or last of which is introduced by or or or whether