It is essential that you grasp a rudimentary understanding of these terms to make changes to your registry. All of this information can be found if the RFC which is very technical reading and you really do not need to go there just to setup your system to get the optimal usage. It is the largest amount of data that can be transferred in one physical frame. It determines whether fragmentation will occur if the frame rate is too small. It defines the largest segment of TCP data that the Winsock will accept.
Networks agree to to use the smaller of each end's value.
It determines how much data your computer is prepared to receive. It will also cause your system to be very slow if it is set too small. It is a matter of mixing, matching and deciding how you want to use your system. If you are going to use a lot of screaming video and audio, keep these as close to the RR specs as possible. It is the only place I have found where maximizing the setting causes a problem.