The Jump command allows selected few units to traverse terrain by temporarily entering air-space. Most of Jumpbots, Dirtbags and Recon Commander are able to jump (also, Lobsters attack has mechanics which work in a similar way). Default key is "J".
Jump provides big tactical advantage, for both traversing terrain, retreating, atacking from unexpected angles and more. Jugglenaut can use its jump to directly inflict damage. Beware, that while jumping units have several vulnerabilities, such as being targeted by Anti-Air Defences, easily read landing location and inability to change course, weakness to physics-based weapons like Newton turrets.