“Stretch assignments are those that require someone to manage and negotiate change, exert influence over others, and build coalitions. ... These assignments are highly developmental because they require new managers to learn new skills in order to be successful in the assignment and they have significant challenge which motivates new managers to work hard to improve their capabilities.”

“Stretch assignments”—experiences which challenge and potentially broaden a person’s current capabilities

The above is quoted from the University of Maryland, Robert H, Smith School of Business website.