Longitudinal is a geometric term of location which may refer to: Longitude Line of longitude, also called a meridian Longitudinal engine, an internal combustion engine in which the crankshaft is oriented along the long axis of the vehicle, front to back Longitudinal mode, a particular standing wave pattern of a resonant cavity formed by waves confined in the cavity Longitudinal redundancy check, in telecommunication, a form of redundancy check that is applied independently to each of a parallel group of bit streams. Longitudinal study, a research study that involves repeated observations of the same items over long periods of time — often many decades Longitudinal voltage, in telecommunication, a voltage induced or appearing along the length of a transmission medium Longitudinal wave, a wave with oscillations or vibrations along or parallel to their direction of travel Longitudinal/longitudinally are also anatomical terms of location..