Deuteronomy 23:2

Mamzer, &c. The author of the Vulgate adds the explication of mamzer, which only occurs again, Zacharias ix. 6. It may in both places denote a stranger, or one of a different religion from the Jews, as Jephte was the son of a prostitute, (Judges xi. 1,) and yet became a judge of Israel. But strangers, as long as they professed a false religion, could not be entitled to the privileges of Jewish citizens; and even after they had relinquished their false worship, they were bound to wait ten whole generations, or a long time, before they could fill the posts of honour and command. (Calmet)

This, however, seems to be contrary to the disposition made in favour of the Idumeans and Egyptians, who were admitted in the third generation. A mamzer may, therefore, be (Haydock) a bastard of a different nation from the Jews, (Menochius) which was not the case of Jephte. (Haydock)

The Rabbins specify three sorts of mamzers: 1. those born of parents who, by the law, are forbidden to marry, being too near akin; 2. those who are the fruit of adultery, or some criminal commerce, which is punished with death; and 3. those whose birth subjects the parents to be cut off or retrenched from the people. (Selden, Jur. v. 16.)

The Septuagint, &c., exclude the children "of a harlot," which is the sense of mamzer in the canon law. The Christian Church rejects such from holy orders, and the Athenians would not suffer bastards to offer sacrifice in the city, but only in the Cynosarge, dedicated to Hercules, whose birth was hardly legitimate. In a word, some understand that mamzer comprises all concerning whose birth any doubts might be entertained. (Calmet)