Prima facie is a Latin expression meaning "at first sight," used in common law regions to denote a case that is strong enough to justify further discovery and possibly a full trial.
For example, being found standing near a dead gunshot victim with a smoking gun in your hand would establish a prima facie case for murder.
Prima facie is often confused (even by legal scholars) with res ipsa loquitur (the thing speaks for itself), the legal doctrine which establishes that the evidence on its own is sufficient to establish the fact in question unless it is explicitly rebutted by other evidence or mitigating circumstances.
See also