Hi
The term gaussian is related to the probability distribution of noise voltage level that it's described by a gaussian curve.
This kind of noise is generated by thermal effect in resistor, attenuation and other passive devices.
If you connect a scope to the output of any circuit you will found a (very low) noise level depending on gaussian noise and other kinds of noise (like flicker noise); if you will able to register istant values of noise voltage in a long time you will plot a gaussian plot.
Angelo.