The orderly movement of a motor neuron from one site to another. A motor neuron is an efferent neuron that passes from the central nervous system or a ganglion toward or to a muscle and conducts an impulse that causes movement. [ http://purl.obolibrary.org/obo/CL_0000100 http://www.ncbi.nlm.nih.gov/pubmed/20711475 GOC:yaf ]