I would call it a community decision to pick one deserving post to reward with the combined voting power of all Steemvoter users who choose to participate in our guild. It's our way of helping authors who may not be receiving the attention or recognition they deserve for their hard work. And yes, you are not allowed to nominate yourself.

Steemvoter is basically a voting robot (we call them bots) that is available for anyone with a Steemit account to use. You have to sign up for our service on https://steemvoter.com/ and then you can setup voting rules to auto-vote your favorite authors. Note that you do not have to participate in our guild vote nominations to use Steemvoter.

Some people prefer manual curation to auto curation with a bot. We think it's best to take a mixed approach combining both manual & auto curation. There is nothing inherently wrong with using a bot; you won't get banned or kicked out of Steemit or anything. Steemvoter has hundreds of users; it's simply another tool in your Steemit toolbox. But like any tool, it has to be used properly to be effective.

This post by @cryptomancer has a more detailed discussion and gives a nice introduction to the service: https://steemit.com/steemit/@cryptomancer/steem-voter-review-bringing-bot-power-to-the-masses