A bio-survey was a study done by Starfleet officers on alien worlds.
In 2372, Dr. Julian Bashir and Chief Miles O'Brien performed a bio-survey on Merik III, a planet in the Gamma Quadrant while on the runabout USS Rubicon. (DS9: "Hippocratic Oath")
Later that year, O'Brien had upgraded the sensors of a runabout, so according to him the scan resolution was good enough to perform an entire bio-survey from orbit. (DS9: "The Quickening")