The adjective captivating describes something that's completely enthralling and holds your attention. You might find a marathon of episodes of a TV show so captivating that you forget to eat dinner.
When people are captivating, they're often very intelligent, attractive, charming, or otherwise fascinating. Something that catches and holds your interest is captivating, like a captivating mystery novel you just can't put down. In fact, this adjective comes from the Latin captivatus, "to take or capture," and early in its use, captivating had that literal meaning. Now it's only used to mean capturing interest.