What do christians mean by confirmation?
The sacrament is there in scripture in acts 4:27 , and referred in early fathers.
E.g. Tertullian,around 200 - pre New Testament canon - says even by his time it was an ancient rite, a part of sacred tradition, he said and I quote:
"Then having gone up from the bath we are anointed with a blessed anointing of ancient discipline, by which people were accustomed to be anointed for priesthood, by oil from a horn from which Aaron was anointed by Moses [
Ex 30:22-30]. For this reason we were called “christs” (“anointed ones”) from “chrism,” which is the ointment which lends its name to the Lord. It was made spiritual because the Lord was anointed with the Spirit by God the Father, as it says in Acts: ‘For they were gathered together in that city against your holy Son whom you have anointed [
Acts 4:27].’ Thus also the anointing flows on us physically, but benefits spiritually, as the physical act of baptism (that we are immersed in water) has a spiritual effect (that we are free from transgressions). Next, calling and inviting the Holy Spirit, the hand is imposed for the blessing.”
Many Others in similar vein e.g. Hippolytus around 200
“The neophytes are anointed by the presbyter from the oil consecrated by the bishop. He says, ‘I anoint you with holy oil in the name of Jesus Christ.’ And thus, drying themselves, the individuals are vested, and afterwards are brought in the church.
“But the bishop, imposing his hand on them, prays by saying, ‘Lord God, who made them worthy to merit the forgiveness of sins by the bath of rebirth of the Holy Spirit, send your grace onto them, that they may serve you according to your will. For to you is the glory, to the Father and to the Son with the Holy Spirit in the Holy Church, both now and for ever. Amen.’
“Afterwards, pouring the consecrated oil from his hand and imposing it on the neophyte’s head, let him say, ‘I anoint you with holy oil in the Lord, the Father Almighty, and Christ Jesus, and the Holy Spirit.’
“And consigning the neophyte on the forehead, let him offer the kiss and say, ‘The Lord be with you.’”