What do the specs on a wind turbine really mean?

I was looking at a wind turbine that was advertised as being capable of producing 3KW.

Voltage: 48V Maximum output: 3000 Watts
Working wind speed: 3~25 m/s
Rated RPM: 450 r/m

In general, if the maximum output is 3,000 watts, what should the continuous output be? I am assuming that the maximum output would occur at 25 m/s? Should there be a chart included with each turbine showing the output at various wind speeds? A windmap for the region where I am shopping for land says that it is in the 12m/s band.

A 3000 watt generator rated at 48 Volts would have to produce 62.5 Amps at the rated RPM.
If your wind speed was half of the rated speed, you should expect something like one quarter of the output wattage.
This is not an accurate calculation as it is probably even less than that, I would have to find the exact specs for your set up, as it probably could not reach half of the 450 RPM with half the wind speed.