A stem (or "stemming") is a body position where the climber presses their feet against two opposing walls or features — typically the two faces of a corner or chimney — and uses the opposing pressure to support their weight. The legs spread out wide and push outward, creating enough friction and counter-force to take weight off the arms entirely.
Stemming is the dominant technique in dihedrals (inside corners) and chimneys, where the rock geometry actively encourages the body to spread. A good stem can let the climber rest indefinitely with minimal upper-body engagement — ideal for chalking up, recovering on a long route, or strategising the next move on a cruxy section.
Flexibility helps — climbers with limited groin or hip mobility struggle to spread wide enough for the most useful stems. Fortunately, stemming is one of the most trainable techniques: regular stretching, dedicated stemming routes at the gym, and outdoor crack climbing all build the necessary range and trust. Look for any indoor route with a corner feature — those are the gym's stemming classroom.