In work, a sideways move is a change of job at the same level. A sideways move, move sideways, a sideways step.
It is neither promotion nor demotion, and it is often the polite description of one of them. Genuine sideways moves are how people broaden experience. As an adverb, sideways means to or from the side: turn it sideways, look at somebody sideways. A sideways glance is one given without turning the head, and it usually means doubt. Note knock somebody sideways, meaning to shock them completely.
From side + -ways.
Etymology from Wiktionary, CC BY-SA
Practised in Work & Careers