Jogger comes from 'jog' + '-er'; 'jog' is late Middle English, of unknown origin, perhaps a variant of 'shog' ('to shake, jolt'). As a noun, jogger means a person who runs at a steady, gentle pace for exercise. The same family is visible in related forms such as jog and jogging. Morphologically, the word is built from the elements named in its history, so the modern form preserves a visible compound, prefix, or suffix structure. The uncertainty belongs to the older derivation, so the explanation should preserve alternatives rather than choosing one unsupported origin.