Low pass filter   

A filter which attenuates frequencies above its cutoff frequency (which is the point where the signal is 3 dB down).  

The slope of the filter is the rate of attenuation, i.e. 6, 12 or 24 dB per octave.

Also known as “Q”, the resonance of a filter is the measure of the amount of feedback from the filter’s output to its input.  Filters with high “Q” will amplify the signal at the cut-off frequency and thereby narrow the filter’s effective bandwidth A good example of a filter with a high Q is a wah wah pedal for the guitar:  the familiar “wah” is the sound of a swept low pass filter with high Q.  Some filters permit the Q to increase to the point of feedback, at which point the filter becomes a sine oscillator.
Example is a sawtooth wave into low pass filter with high Q or resonance.  Note how the harmonics of the sawtooth are made prominent. low pass filter
see hi pass filter