What does "beg the question" mean?

Take for granted or assume the truth of the very thing being questioned. For example, Shopping now for a dress to wear to the ceremony is really begging the question—she hasn't been invited yet. This phrase, whose roots are in Aristotle's writings on logic, came into English in the late 1500s. In the 1990s, however, people sometimes used the phrase as a synonym of “ask the question” (as in The article begs the question: “What are we afraid of?”).