level-off altitude

altitude above ground level

minimum off-route altitude

depot maintenance (beyond O and I level activities, performed in an industrial-type facility) / D-level maintenance

level(l)ing-off

noise level as a function of take-off mass

off-route (off route)

off-design / off design

lift-off / lift off

on-off keying; on/off keying (OOK)

altitude

altitude barrier

altitude dial

altitude performance

altitude separation

cruising altitude

gain altitude

high altitude

high altitude-high opening (HAHO)

high altitude-low opening (HALO)

high- and low-altitude surveillance

high-altitude long-endurance (HALE)

high-altitude low-opening parachute technique (HALO)

high-altitude nuclear burst

keep-out altitude

low altitude parachute extraction system (LAPES)

operational altitude

relative altitude

subsonic low altitude cruise missile

surveillance, high- and low-altitude surveillance

theater high altitude air defense (THAAD) system

transition altitude (TA)

Height Above Ellipsoid (HAE); altitude / elevation above the ellipsoid (ellipsoidal height)