刻骨铭心永记在心
[kè gú míng xīn yŏng jì zài xīn]
It means 'carve into the bone and engrave into the heart forever', signifying memories so intense and profound that they never fade away. It indicates significant, impactful experiences—often referring to intense romantic feelings—that have been etched deep into memory, suggesting everlasting remembrance or commitment.