Okay kiddo, so you know how we measure time in hours, right? Well, in Jewish law, there's something called "relative hour".
Basically, it means that the length of an hour can change depending on what time of year it is. During the summer, when the days are longer, an hour is longer. And during the winter, when the days are shorter, an hour is shorter.
This is because in Jewish law, certain activities have specific times they can or can't be done. For example, certain prayers can only be said during certain times of the day. So it's important to know how long those specific times are, which is why the length of an hour can change.
So, relative hour is just a way of measuring time that takes into account the changes in daylight throughout the year. It helps people know when they can do certain things according to Jewish law.