"Completed" just means that the ICO is no longer running (the company is no longer generating/selling new tokens). If the tokens have a price in that list, it'

"Completed" just means that the ICO is no longer running (the company is no longer generating/selling new tokens). If the tokens have a price in that list, it's because people are buying and selling them and value them for some reason. Maybe the tokens have direct utility for doing things in some decentralized smart-contract-based system, or people believe that such a system is arriving in the future based on word of the dev team. The tokens with no listed value now probably aren't being traded by anyone and aren't being valued by anyone, and it's probably because the plan for the system they were set up for turned out to be vaporware / devs ran off / devs never really existed / people lost faith in the devs / the idea turned out not to be feasible or need tokens at all, etc.