Definition of Magick

The conscious manipulation of the soul to create change.

Magic could be both the theoretical-practical system and the spell or ritual, although this latter may be included in the practical part.
It has thin borders with occultism and esotericism in their respectively lower and higher sense. For example, initiation (especially) is where magic meets spiritual growth.
Likewise, at the core it doesn’t change, but this ancient core is also the “not divided knowledge”; science evolved, there is a scientific part of magic as well.