The Greek adjective bebēlos means profane, unhallowed, accessible to all (hence common/unclean), or godless. The word originally described a threshold (bēlos) that could be stepped on — i.e., something not set apart but open to ordinary use. Over time it came to mean anything stripped of the sacred, desecrated, or irreligious.
Paul uses bebēlos in 1 Timothy and 2 Timothy to describe "profane and vain babblings" and "profane myths." Esau is called bebēlos in Hebrews 12:16 — one who treated the sacred (his birthright) as something ordinary, exchangeable for a bowl of stew. This is the essence of profanity in the biblical sense: treating the holy as if it were merely common. Every generation faces Esau's temptation — to trade eternal for immediate, sacred for convenient. Bebēlos warns against the slow drift of casualness toward holy things.