It is Latin, it is spelled “Confiteor”, and it means “I confess”.
It is one of the four options for the penitential rite during the Novus Ordo holy mass:
OPTION 1 - The Confiteor
All present: I confess to almighty God, and to you, my brothers and sisters, that I have sinned through my own fault, in my thoughts and in my words, in what I have done, and in what I have failed to do; and I ask blessed Mary, ever virgin, all the angels and saints, and you, my brothers and sisters,to pray for me to the Lord, our God.
OPTION 2 (This one is rarely used)
Priest: Lord, we have sinned against you: Lord, have mercy.
Congregation: Lord, have mercy.
Priest: Lord, show us your mercy and love.
Congregation: And grant us your salvation.
OPTION 3 - Led by the priest or a deacon
P/D: (First invocation*): Lord, have mercy.
Congregation: Lord, have mercy.
P/D: (Second invocation*): Christ, have mercy.
Congregation: Christ, have mercy.
P/D: (Third invocation*): Lord, have mercy.
Congregation: Lord, have mercy.
(*The invocations are often things like; “You come to heal the contrite”, or “You plead for us at the right hand of the Father”)
OPTION 4 - The Kyrie
P/D/Cantor/Choir: Lord, have mercy.
Congregation: Lord, have mercy.
P/D/Cantor/Choir: Christ, have mercy.
Congregation: Christ, have mercy.
P/D/Cantor/Choir: Lord, have mercy.
Congregation: Lord, have mercy.
The Penitential rite concludes with:
Priest: May almighty God have mercy on us, forgive us our sins, and bring us to everlasting life.
Congregation: Amen
After using option 1 or 2, the priest should go immediately to the Kyrie, but not after option 3, since the Kyrie is fully incorporated into that option. Option 4, using just the Kyrie, is quite rare, but acceptable.
I hope I answered your question!
MT