What does 18K CE mean on inside of ring?

"18K" indicates that the ring is made of 18 karat gold, meaning it is 75% pure gold mixed with other metals for strength and durability. "CE" likely stands for "Conformité Européenne," a marking indicating that the ring meets European Union standards for quality and safety. In summary, "18K CE" means the ring is made of high-quality 18 karat gold and has been certified to meet EU standards.