The Greek adjective byssinos (G1039) means "made of fine linen" or "of byssus" — the extraordinarily fine, white Egyptian or Phoenician linen fabric associated with wealth, royalty, and purity. It appears in Revelation in descriptions of heavenly garments.
In Revelation, byssinos (fine linen) carries profound theological significance. Revelation 19:8 explicitly interprets the fine linen worn by the Bride of Christ: "Fine linen is the righteous deeds of the saints." The purity of the garment is not earned but granted — the righteousness of Christ imputed to His people. This is the justification that clothes every believer in white.