The maximum voltage the relay contact can withstand
The vertical line at 200V means you can switch up to 300mA, at up to 200V, as long as the load is resistive.

A straight line on a log-log graph like this one means a constant product, in this case 60 watts.

The horizontal line at 2A says you can switch up to 30V at that current.

So the relay can be used for resistive loads, as long as it stays within  all three constraints of 2A, 200V, and 60W.