Hey @laxmanmah, great question. Witness are who maintain and keep the Steem blockchain running. They produce the block which contain transactions, posts, comments, upvotes, etc. We also ensure the the blockchain is secure and make some decisions about the future of Steem. So if it weren't for witnesses, there would be no Steem (or Steemit, Dtube, Dlive, etc.). So they're very important. And everyone can vote on who they feel does a great job. :)