What does beg the question mean?

Fowler's Modern English Usage classifies begging the question in a somewhat different fashion (for example, in contrast to the meanings from Merriam-Webster, the Oxford English Dictionary, and the American Heritage Dictionary). Fowler states that it is "The fallacy of founding a conclusion on a basis that as much needs to be proved as the conclusion itself." This is more commonly known as the Fallacy of many questions.