Flight was the ability to move oneself through the air.
In 2266, a polywater intoxication-affected Joe Tormolen ranted about the futility of space exploration, claiming "If a man was supposed to fly, he'd have wings." (TOS: "The Naked Time") Later, while discussing the risk of hosting the minds of the Arretans in 2268, James T. Kirk noted that people used to say that, adding, "But he did fly. He discovered he had to."