Literally, using ice tools (axes) and crampons to climb ‘dry’ rock as opposed to ice or snow.
Dry-tooling initially gained popularity as a way of training for ice climbing, but has evolved into a sport in its own right. Today, dry-tooling generally features bolted protection and usually involves no ice at all (particularly in the UK), so in many ways it is more akin to sport climbing than ice climbing. Unlike ice climbing, dry-tooling also has the advantage that it can be done all year round, often whatever the weather.
Dry-tooling trains precision and balance on delicate placements and footholds, as well as giving a good arm workout, and may necessitate flexibility on more gymnastic moves. Easy access, reliable protection and a lack of objective hazards frees climbers to enjoy the challenge of pure technical difficulty, like in sport climbing.