Hatafat dam brit is a procedure performed under the following specific circumstances:
— a baby who is circumcised in the hospital (for whatever reason) without a proper brit milah ceremony having been performed
— an adult who has already been circumcised but who has not had a brit milah ceremony. This was the case for many Russian Jews who came to the United States and Israel in the 1990’s and thereafter. Such individuals who had never been circumcised and who wanted to do so to be in conformation with Jewish law had to undergo adult circumcision under anesthesia while having the brit milah prayers said by special arrangement.
— a convert to Judaism who has already been circumcised
Hatafat dam brit involves drawing a drop of blood from the penis while performing a religious ceremony similar to that of the brit milah. It is a rite of ritual purification.
The origin of this procedure and its rationale is this: A brit milah is much more than a medical circumcision; removal of the foreskin constitutes only one part of the mitzvah. The purpose of performing a bris is to enter a boy (or man) into the Covenant of Israel. This is what performing the service of hatafat dam brit does in the case of babies, boys, and men who fall under the categories mentioned above.