System load is a measure of the activity of your CPU. The 1, 5, 10 minute averages are the same output that you get from running the 'uptime' command. I have no idea what the units are as they don't seem to match up with the Min, Max, Avg, Last values.
Processes would presumably be a measure of how many programs are running (there is usually a lot of background stuff going on even when you aren't using a computer), but this always seems to be pegged at (going from memory here) 300 jobs.