What is Time?

What is time? Every single day people say the word, yet, does anyone know what it is? We measure events with time, we organize things by time, but what is it? What is a day? A period of time where the sun rises and sets. A second is currently defined as 9,192,631,770 periods in the transition between two hyperfine levels of ground state in the cesium-133 atom. It is fairly obvious that a unit of time is simply an observed period of time in which change occurs. We then measure our own change in terms of known quantities, such as day, hour, second, minute, year, etc. Each is simply an observed period of change, and by applying the titles of second, minute, hour, etc, we improve efficiency and speed up whatever it is we're trying to figure out or explain. Imagine trying to explain to someone what a second is, without being able to use any titles of periods of change. Life would literally be slowed down to a crawl. It is a work of necessity, and one that serves humanity very well. So, what is time? Time is change. Time is an illusion, it doesn't exist. It is just a name we give to help us measure how fast something changes in relation to a universally known constant period of change.