A person was a sentient individual. Miranda Cleaves and her colleagues debated whether or not the gangers were people. The Eleventh Doctor stated that they had become so. (TV: The Almost People)
When the Ninth Doctor accused the Lady Cassandra O'Brien.Δ17 of murdering people, all of whom were non-humans, aboard Platform One, Cassandra retorted that it depended on his definition of people, which she claimed was enough of a technicality to keep lawyers dizzy for centuries. (TV: The End of the World)