The Greek noun Hebraios (Ἑβραῖος) means 'a Hebrew' — a person of Hebrew descent, culture, and language. In the New Testament it appears in Acts 6:1 (distinguishing Hebrew-speaking from Greek-speaking Jewish believers), 2 Corinthians 11:22, and Philippians 3:5 (Paul's claim to authentic Jewish heritage).
Paul's threefold claim in Philippians 3:5 — 'a Hebrew of Hebrews' — is one of the New Testament's most intense statements of ethnic and religious identity. By 'Hebrew of Hebrews' Paul likely means he maintained the Hebrew language and customs even in a Greek-speaking diaspora context, a point of pride for conservative Jews. Yet immediately Paul declares all this 'rubbish' compared to knowing Christ (Philippians 3:8). This is not anti-Semitism — it is the proclamation that covenant identity finds its ultimate meaning in Christ, not in ethnic heritage. Abraham was declared righteous before circumcision (Romans 4:10), and the true children of Abraham are those who share his faith.