Kneeling was the act of standing on one's knees. It was done as an act of submission, particularly in prayer, or honor.
In 2268, Elaan noted that the crew of the USS Enterprise had her permission not to kneel in her presence. (TOS: "Elaan of Troyius")
In 2366, Jean-Luc Picard told Nuria not to kneel to him. Nuria assumed he did not want her to, but Picard told her he did not deserve it. (TNG: "Who Watches The Watchers")
In 2373/2374, a hologram of Leonardo da Vinci admitted that even he found himself kneeling in prayer before God. (VOY: "Scorpion")