Protection of wiring

1.) What exactly is the definition of exposed wiring? Is it considered to be any wire or cable without conduit?
2.)What is a running board for running cable across joists?
3.) Can cable be run and attached along the length of the joist or just across?
4.) If just across, it sounds like it must go through holes drilled in the joist rather than attached to the bottom. Is this correct?
5.)Is NM acceptable wiring in cabinets?