A conversion factor is a number by which we multiply one unit, a meter of length for example, to get that same length expressed in other units, centimeters for example. In this case the conversion factor is 100. Multiply 10 meters by 100 centimeters per meter to get 1000 centimeters. The conversion factor may be decided by tradition, committee work or Nature. The conversion we are interested in is that from seconds to meters.

For centuries it did not occur to anyone to try to convert time to distance. Then Einstein, Minkowsky and that gang started fooling around with relativity and thought it would be convenient to express time and distance in the same units. They were not at liberty to decide how many meters equal a second because, given the existing definition of a meter and a second, that conversion factor was already decided by nature. Meters per second (m/s) is speed and Nature has a favorite speed, that of light. So rather than base the conversion on a speed that was different in different reference frames, they went with 299,792,458 m/s. We will customarily round that off to 300,000,000 m/s for convenience. So 1 second = 300,000,000 meters and 1 meter = 1/300,000,000 seconds.