tvaziriatpfm These days it is mostly marketing but historically there was a difference. All-wheel-drive is historically associated with automated systems that shift power from front-to-rear based on slip and conditions. Four-wheel-drive allows *driver* control of which wheels are driven.
tvaziriatpfm In the 2010s, pretty much every system became capable of automatic operation, so it is now a marketing term where 4WD denotes higher capability systems (those designed for off-road use as opposed to just snow and ice)