Oblique photograph
Photograph acquired with the camera intentionally directed at some angle between
horizontal and vertical orientations.

OMS
Orbital maneuvering system.

Orbit
Path of a satellite around a body such as the earth, under the influence of gravity.

Orthophotograph
A vertical aerial photograph from which the distortions due to varying elevation, tilt, and surface topography have been removed, so that it represents every object as if viewed directly from above.

Overlap
Extent to which adjacent images or photographs cover the same terrain, expressed as a percentage.