Nomina sacra
In Christian scribal practice, nomina sacra (singular: nomen sacrum from Latin sacred name) is the abbreviation of several frequently occurring divine names or titles, especially in Greek manuscripts of Holy Scripture. A nomen sacrum consists of two or more letters from the original word spanned by an overline.

Metzger lists 15 such expressions from Greek papyri: the Greek counterparts of God, Lord, Jesus, Christ, Son, Spirit, David, Cross, Mother, Father, Israel, Savior, Man, Jerusalem, and Heaven.[1] These nomina sacra are all found in Greek manuscripts of the 3rd century and earlier, except Mother, which appears in the 4th.[2]
Nomina sacra also occur in some form in Latin, Coptic, Armenian (indicated by the pativ), Gothic, Old Nubian, and Cyrillic (indicated by the titlo).