Let's say mountaineering is an all-encompassing word for all sorts of activities. Hiking is a good entry point, but once you get into it, you will soon find yourself getting into technical gear and skills to to be able to get to the top of places that require some sweat.

For example, here's my recent trip with few friends https://www.mountaineers.org/activities/trip-reports/interme... - 2 nights out, roped glacier travel, scrambling, rock climbing, a good mix of planning and stamina was required. And for all I know this is a low end of mountaineering.