Load averages show the system load, i.e. the number of processes using CPU or waiting for system resources (usually CPU and disk). The 3 metrics ldavg-1, ldavg-5, ldavg-15 refer to 1, 5 and 15 minute load averages.

Maximum load average value roughly corresponds to the number of CPUs available for your plan.
For example, if your plan has 1 CPU and your load average is above 1.0 (or if your plan has 2 CPU and your load average is above 2.0), then the server is overloaded and needs to be upgraded to a plan with higher CPU count.