Ortho
Ortho- is a Greek prefix meaning “straight”, “upright”, “right” or “correct”.
Ortho may refer to:

Ortho, Belgium, a village in the Belgian province of Luxembourg

Science
Arene substitution patterns, two substituents that occupy adjacent positions on an aromatic ring
Chlordane, an organochlorine compound that was used as a pesticide

Mathematics
Orthogonal, a synonym for perpendicular
Orthonormal, the property that a collection of vectors are mutually perpendicular and each of unit magnitude
Orthodrome, a synonym for great circle, a geodesic on the sphere
Orthographic projection, a parallel projection onto a perpendicular plane

Medicine
Orthomyxovirus, a family of viruses to which influenza belongs
Orthodontics, a specialty of dentistry concerned with the study and treatment of malocclusions
Orthopedic, the study of the musculoskeletal system
Ortho-DOT, a psychedelic drug
Ortho-cept and Ortho Tri-cyclen, kinds of oral contraceptive drug

Theology
Orthodoxy, right (correct) belief
Orthopraxy, right (correct) action

Business
Ortho Pharmaceutical, which merged into Ortho-McNeil Pharmaceutical before being bought by Johnson & Johnson
Ortho-Clinical Diagnostics, another subsidiary of Johnson & Johnson
Ortho, a lawn care and pesticide company owned by the Scotts Miracle-Gro Company

See also
Orthos (disambiguation)
Ortho Mode Transducer
Orthochromatic
Orthophotography
Orthoptera