On

On, on, or ON may refer to:

• On (Japanese prosody), the counting of sound units in Japanese poetry
• Ön, a 1966 Swedish film
• On (novel), by Adam Roberts
• Air Nauru IATA airline designator ON
• Heliopolis (ancient), an ancient city in Egypt, from a transliteration of its ancient Egyptian name
• ITV Digital, a failed British digital television service originally named ONdigital
• Leg side, in the game of cricket
• Nintendo On, a fake video game console
• Old Norse, a North Germanic language commonly referenced in etymology
• Old Nottinghamian, a person who attended or worked at Nottingham High School
• ON Semiconductor, a leading supplier of power management solutions
• O'Nan group, a mathematical group
• Ontario, Canada
• Ontology, a branch of philosophy that deals with the concept of being
• On'yomi reading of Japanese kanji characters
• Osteonectin, a glycoprotein
• Osteonecrosis
• Order of the Nation, a Jamaican honour
• Overground Network, a railway scheme in South London
• Overmyer Network, an ill-fated US television network
• OS/Net, the OpenSolaris Community
• Optic neuritis, especially relevant in multiple sclerosis