From the Semitic root *b-b, meaning "gateway" or "opening." Cognates appear across the Semitic family: Hebrew בַּיִת (bayit, house), Akkadian bābu (gate), and Aramaic בָּבָא (bābā). The same root famously gives its name to the ancient city of Babylon (Bāb-ilim, "Gate of God") and the Bab el-Mandeb strait connecting the Red Sea to the Gulf of Aden.

In Arabic, بَاب carries rich metaphorical weight. Classical Arabic uses it to mean "chapter" or "section" of a book (as in the chapters of a legal or religious text), so you will often see كِتَابُ الطَّهَارَةِ بَابٌ أَوَّلٌ in Islamic scholarly works. The word also survives in many Arabic place names across the Middle East and North Africa — most notably بَاب الحَارَة (Bāb al-Ḥāra), the hugely popular Syrian TV series whose title literally means "The Neighbourhood Gate," a symbol of community and belonging.