"Weighting":

1) Acoustic noise level is usually measured in order to get an idea of how much it should disturb people.

2) Humans have different sensitivities(perception) for different signals, the main parameters being amplitude and frequency.

3) In order to "simulate" the human perception, there are some standard ways to filter the signal that a microphone is able to grab. Some standards give more "weight" or importance to a range of frequencies, others to a different range, they can use different slopes when filtering, ... and this is what weighting means.

I think a book about acoustics will be of help.

By the way, it is a good idea to be kind with those who spend their time answering our questions, even in the case their answers are not what we expected.

Regards,

Alfredo del Rio.