In traditional [music] theory, the subdominant is the fourth degree of the [diatonic] scale.
The term is also applied to chords whose root is this degree, often 4/3 [ratio] or 500 cents (¢).
In general, the Subdominant is the octave complement of the Dominant.
The subdominant is generally labeled with Roman numeral IV.
The tonalsoft.com website is almost entirely the work of one person: me, Joe Monzo. Please reward me for my knowledge and effort by choosing your preferred level of financial support. Thank you.