The name Perez in the Bible
Judah manages to impregnate her while not realizing who she is (he thinks she is a prostitute). When she shows up pregnant, Judah wants to execute her, but clever Tamar made sure she could prove that Judah was the father. When Tamar gives birth to Perez and his brother Zerah, Zerah is on the way out first but Perez shoves him out of the way and becomes the first-born. Hence it is said of Perez, "What a breach you have made for yourself!" (Genesis 38:29).
Since Perez, not Zerah, is the ancestor of Jesus Christ, many interpreters see a connection between Jacob and Esau, who also swapped the coveted predicate of being first-born (Genesis 25:30-34). The name Perez appears in both genealogies of Christ, and is spelled in Greek as Φαρες, Phares (Matthew 1:3, Luke 3:33).
The ethnonym פרצי, Perezite(s) occurs once in the Bible, in Numbers 26:20.
Etymology of the name Perez
The name Perez comes from the root-verb פרץ (paras) meaning break through:
NOBSE Study Bible Name List and Jones' Dictionary of Old Testament Proper Names agree: The name Perez means A Breach. Jones adds the eloquent Irruption.