dBu
Definition
A voltage-referenced measurement unit used in professional analog audio equipment. 0 dBu equals 0.775 volts RMS. The standard operating level in professional studio gear is +4 dBu; consumer equipment typically operates at -10 dBV.
In Simple Terms
A measurement used by professional analog gear to describe signal level. Most relevant if you're connecting hardware equipment together — mismatching levels between pro and consumer gear creates noise or distortion.
Common Confusion
dBu and dBV are both voltage references but use different zero points. Mismatching equipment operating levels is a common source of unexpected noise or distortion in hybrid analog/digital setups.