OPN may stand for: Osteopontin, a glycoprotein secreted by osteoblasts Object Process Network, a simulation model meta-language Optics & Photonics News, a magazine Oneohtrix Point Never, recording alias of musician Daniel Lopatin Olivary pretectal nucleus, a nucleus in the pretectal area, or pretectum In mathematics, odd perfect number Ora pro nobis, Latin phrase litt. meaning "pray for us", often abbreviated as OpN in prayer books and breviaries Yamaha YM2203, a sound chip