Just the ordinary dictionary definition. Using evidence and arguments to establish a fact or truth.

Of course the arguments and evidence that you use to prove your truth must also be proven themselves, and so and and so forth. No matter what it is you’re trying to prove, there are only three possible outcomes. Circular reasoning, infinite regression, or stopping at an arbitrary point (usually described as an axiom). This is known as the munchausen trilemma.

Although this question has lead me to see that my previous argument is incomplete. It is possible to believe a truth without faith. That is, through ignorance. A failure to scrutinize your belief sufficiently to understand that it is based on an unprovable axiom, and is thus an act of faith. People who debate the merits of science vs religion tend to be ignorant of this, equally on both sides.

Nothing about what I’m arguing is even remotely controversial. It would be a part of any entry level course on logic at any university.