85 dB(A) of Sound

The A-weighted system reduces or "corrects" the sound pressure values (in dB) for lower audio frequencies. This is done to better match the actual hearing performance of the human ear at frequencies below 1kHz, where human sensitivity diminishes as compared to frequencies above 1 kHz.

What are you doing with the number after you have understood it? If you are comparing it to a legislative limit, you will need to ensure you have the correct weighting. If you're looking for the source of an annoying noise, then sometimes A-Weighting is better since, as AH said, it gives a better approximation of the human ears' response than does the raw logarithmic scale.