Begging the question
Etymology
The phrase is a loose translation of the Latin "petitio principii," "a postulating of the starting point," itself rendering Aristotle’s Greek for asking the audience to grant the initial claim. "Begging" here means "assuming without warrant," not "raising." In everyday speech it is now widely used to mean "raises the question," a shift many careful writers still resist.
noun phrase · /BEG-ing thuh KWES-chun/
Assuming the truth of the very conclusion you are supposed to be proving.
What it names
Spotting it reveals arguments that only sound like proof because they quietly help themselves to their own conclusion.
Example
"The scripture is true because it is the inspired word of God, and we know that because scripture says so" begs the question.
Related idea
It is the tight, single-step case of circular reasoning, where the loop from premise to conclusion is one move wide.