Refers to all that is NOT sport climbing: placing one's own gear, attempting a route before climbing or inspecting it on a top-rope.
Evolving as an extension of mountaineering, and close kin to alpine climbing in perspective and motivation, traditional rock climbing involves placing removeable protection in cracks and pockets or around natural features (such as trees or chickenheads) to secure the climber in the event of a fall. Strict traditionalists, or trads as they are called, eschew the use of bolts or other items that may permanently mar the rock (though pitons, which saw heavy trad use in the past, have done their part to assist Mother Nature's erosion efforts).
Rock climbing using protection placed by the climber on lead and removed by the second.