RTD is an abbreviated term for retired. It is used in a boxer's official fight record to indicate that the referee had stopped the bout during the minute rest period between rounds. The referee may have done so using his own or the ringside doctor's judgment, or when a fighter indicated during the rest period that he did not want to continue to the next round. Thus, for example, if a boxer quit during the rest period after the third round, BoxRec will record it as RTD-3.
RTDs usually are often recorded as a technical knockout (TKO), and are included in a boxer's knockout total in his official record.