What do Watts mean on a light bulb?

That means how much power the light bulb is consuming all the time when it's on.
Incandescent lightbulbs have one wattage rating, but the new CFL and LED lightbulbs have two wattage ratings:
  1. wattage - this is the actual power consumed
  2. equivalent wattage - this is the wattage that would be consumed by an incandescent lightbulb that produced the same amount of light