Hey Alex, hey all,
Also there is a big difference whether it is a number that designates a router or a spindle. A router is a power tool, which often is rated by simply multiplying the current it draws with the voltage to obtain a power in Watts and to sell it with this rating. A spindle, on the other hand, is not a tool, but a motor, which is made to be the component of a machine, and motors have to comply to IEC 60034-1, which says, the mandatory power rating on the nameplate has to tell the mechanical power available at the shaft, not the electrical power draw. Otherwise engineers would not be able to compare motors, because motors have different efficiency. Of course the electric power a motor draws is much higher as the mechanical power it can deliver, but for choosing a motor for an application, it’s the mechanical power at the shaft that you want to know. The electric power it draws is then important for dimensionating the supply circuit.
Usually on routers and other power tools, their manufacturers don’t tell you the mechanical power the motor can deliver, you just have the electrical power draw. Sufficient to size your circuit and wires, but says nothing about the motor’s efficiency.
See also an example here.