What is Planning?
Planning, like learning, is a focus of AI research. Whereas learning is about choosing where to place a dividing line to separate things, planning is about choosing, and often ordering, a combination of things. The things of interest to planning algorithms include the moves in a chess game and the arrangement of boxes that best fill a constrained cargo space.
One synonym for planning might be "optimization." Optimization strategies often involve some sort of search over the possible combinations. Planning algorithms become interesting, and challenging, once the number of possible combinations becomes too large to evaluate every one. When that happens (and it often does!), some sort of efficient search strategy is needed to pick a good combination without looking at all possibilities.
Machine learning as a research topic is almost exclusively contained within AI. In contrast, many fields, most notably Operations Research and Computer Science, have contributed to the development of advanced planning algorithms.
Planning and Mobile Robots