OR Tambo District Municipality
OR Tambo International Airport
Orthalicus reses
Orthodiagonal quadrilateral
Orthodox Autocephalous Church of Albania
Orthodox Christianity
Orthodox Church in Communist Romania
Orthodox Judaism outreach
Orthodoxy Cognate PAGE Society
Orthodoxy in Estonia
Orthogastropoda
Orthogeomys
Orthogonal array
Orthokeratology
Orthomolecular psychiatry
Orthomyxoviridae
Orthopedic cast
Orthopraxy
Orthotropic material
Orto botanico di Palermo
Orton-Gillingham
Orton Plantation
Ortze