+4 dBu and -10 dBV are both units of measure used to express the strength or level of an electrical signal. The difference between them is the reference level against which the signal level is measured.
+4 dBu is a measurement of the level of an electrical signal relative to a reference level of 0.775 volts. This reference level is commonly used in professional audio and video equipment, and is often referred to as "pro audio level."
-10 dBV, on the other hand, is a measurement of the level of an electrical signal relative to a reference level of 1 volt. This reference level is commonly used in consumer audio and video equipment, and is often referred to as "consumer level."
In general, the -10 dBV reference level is lower than the...