The sound power level describes the sound emission of a sound source objectively, i.e. without any dependence on the distance between the source and the listener or the acoustic conditions of the room in which this source is located.

The sound power level corresponds numerically to the sound pressure level that would be measured on a sphere with a surface area of one square metre if the sound source were a point in the centre of this sphere.

The sound power is the cause, the perception (the sound pressure) corresponds to the effect.

This is directly comparable to the electrical output of a light bulb: the output of a 60-watt light bulb does not change if it is viewed from a greater distance or if it shines in a bright instead of a dark room. A sound source initially emits only direct sound. If the source is located indoors, the sound is partially absorbed by the walls. The part that is not absorbed is reflected and contributes to the listening experience. The proportion of absorbed sound is indicated by the equivalent absorption area of the room.

[Wikipedia / Further explanation: en.wikipedia.org/wiki/Sound_power]