In common use, the word noise means unwanted sound or noise pollution.
In electronics noise refers to the electronic signal in an audio system.
Thermal noise is generated by thermal agitation of electrons in a conductor.
A resistor makes noise without any voltage applied to it.
Temperature ϑ   ° Celsius
Used bandwidth Δ f   Hz
Resistance R   ohms
   
               
   
 RMS Noise voltage Vn   μV (microvolts) 
Noise level Lu   dBu 
Noise level LV   dBV 
Formula for the RMS noise voltage:   Fornula-image Rauschspannungs-Formel

Noise voltage level (audio) LV:
dBu
 ↔ Noise voltage (audio)V:
µV (microvolt)
Noise voltage level  Noise voltage
Reference voltage V0 = 0.7746 Volt = 774 596.67 µV ≡ 0 dBu
Noise voltage level LV:
dBV
 ↔ Noise voltage V:
µV (microvolt)
Noise voltage level  Noise voltage
Reference voltage V0 = 1.0 Volt = 1 000 000 µV ≡ 0 dBu