The term decade comes from the Greek and represents an interval of 10:1.
The decade is used for frequency and level specifications, where the higher frequency has ten times the value of the lower frequency: 100 Hz to 10 Hz or 3 GHz to 300 MHz. In level specifications, the higher level has ten times the value of the lower level. Level drops such as occur in filter curves are also often specified in decibels per decade, for example 20 dB/decade.
There is a direct correlation of a factor of 3.33 between decadal and octave quantities, according to which a level drop of 6 dB/octave corresponds to one of 20 dB/decade. The decadic division is particularly suitable for logarithmic representation.