Noise terminology explained Decibels

SPL = Sound Pressure Level (in dB or dB(A))

Frequency weighting, dB(A), dB(C), dB(Z)

dB(A) – weighting factor which takes in consideration the sensitivity of the human hearing. As our body perceives high frequency sounds more disturbing than low frequency sounds, the dB(A) weighting was introduced. This way, a higher dB(A) level always sounds louder for humans than a lower dB(A) level.

dB(C) – weighting gives more emphasis to low frequencies

dB(Z) – is also called unweighted, linear or flat, no weighting is applied

sound weighting graphs decibel

LAmax = The maximum level with A-weighted frequency response in Fast or Slow time constant.
LAmin = The minimum level with A-weighted frequency response in Fast or Slow time constant.
Lpeak = The true peak level in sound pressure (without time constant), typically a Lpeak will be 3 dB higher than Lmax

1/1 octave filtering – frequencies of measured sound divided in octave bands filtering

1/3 octave filtering – frequencies of measured sound divided in third octave bands filtering

Leq = equivalent sound pressure level over a given time, equivalent continuous sound level

moving Leq = running Leq – the running or moving equivalent continuous sound level

L10 – the sound level that is exceeded 10% of the time

L90 – the sound level that is exceeded 90% of the time

Lxx – the statistical value of the sound level that is exceeded xx% of the time

More info at WikiPedia

Example of sound level: