Ortho (from the Greek word ὀρθός meaning "straight" or "correct") may refer to:
In science
- An arene substitution pattern in which two substituents occupy adjacent positions on an aromatic ring
- Chlordane an organochlorine compound that was used as a pesticide
- Ortho Mode Transducer, is a waveguide component
- An Orthochromatic spectrum is any spectrum of light devoid of red
In cartography
- Orthophotography, aerial photography
In mathematics
- Orthogonality
- Orthonormality
In computer science
- Orthographic projection, a means of representing a three-dimensional (3D) object in two dimensions (2D).
In medicine
- Orthomyxovirus - family of viruses to which influenza (causative agent of the flu) 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
In theology
- Orthodoxy, right (correct) belief
- Orthopraxy, right (correct) action
Corporations
- Ortho Pharmaceutical, which merged into Ortho-McNeil Pharmaceutical before being bought by Johnson & Johnson
- Ortho-Clinical Diagnostics, another subsidiary of Johnson & Johnson