The time required for a planet to complete one turn on its axis is called a what?

It can be called a couple of different things because, believe it or not, "one turn on its axis" can mean two different things. Without getting into a long explanation, here are the basics. You can do more study if you want more details. If you are considering the rotation (turning on the axis) of earth, and you are talking about the earth rotating from one solar noon to the next solar noon, (the moment when the sun reaches its highest altitude), then you are talking about the synodic period of rotation. You are defining a rotation according to earth's relationship to the sun. The earth has to turn more than 360 degrees in order to complete a synodic rotation. In brief, this is because earth is orbiting the sun at the same time that it is rotating on its axis. Over a year these rotations take, on average, 24 hours each. The periods of synodic rotations, therefore, are called days. If you are considering the absolute rotation of earth on its axis, the way the rotation would be seen from the distant stars, then you are talking about earth's sidereal period of rotation, its absolute rotation independent of the sun. This rotation takes roughly 23 hours 56 minutes and 4.1 seconds to complete.