In 'common-practice' harmony, modulation refers to a change of key.
A modulation is distinguished from a tonicization in that the latter gives a more temporary feeling, while a modulation provides a clearly established arrival into the new key, usually for a somewhat extended period of time.
Modulation is ordinarily used in 'classical' music to delineate various different sections of a particular form, especially sonata form.
A change of tonic, mode, or genus is termed modulation in Greek music theory.
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.