It is not simply a medical procedure. It is a covenantal ceremony.
Brit milah means covenant of circumcision
My Jewish Learning explains that brit milah literally means covenant of circumcision and traces the ritual to Genesis, where circumcision is given to Abraham and his descendants as a sign of covenant.
That origin is what gives the rite its enduring force in Jewish thought.
The ritual is traditionally performed on the eighth day
My Jewish Learning notes that the ceremony ordinarily takes place on the eighth day of a baby boy's life, unless health concerns require delay.
This is one of the clearest places where Jewish ritual ties body, time, and covenant together.
The rite is performed by a trained mohel
Chabad explains that the person who performs the ritual circumcision is the mohel, who is trained in both the practical and religious aspects of the rite.
That matters because brit milah is not treated as a mere procedure with symbolic language added on. The ritual expertise is part of its religious meaning.
Why it still matters
Brit milah still matters because it makes Jewish covenantal belonging material and public. The ceremony is not only about ancestry or belief. It is about being entered into a people through a commanded act.
The shortest accurate answer
Brit milah is the Jewish covenant of circumcision, traditionally performed on the eighth day as a sign of entry into the covenant of Abraham.