Quadratic Voting is a way for groups to make decisions together that achieves the greatest possible good for the greatest number of group members.
Groups usually make decisions using majority rule, with everyone getting one vote on every issue. This stops people from being able to accurately and fully express themselves when an issue is particularly important to them. QV instead uses the market principles of budgeting and pricing to let people express what matters most to them.
Individuals have a budget of Credits to allocate among multiple decisions, alternatives, or priorities. One vote costs one credit, two votes four, three votes nine, etc. This increasing cost discourages individuals from putting all their credits on the one issue they care most about. By making the cost of the next vote proportional to the number of votes bought, QV encourages individuals to exert influence exactly in proportion to how much the issue matters to them.
This is why Weyl and Lalley have proven that, like the market economy for private goods, QV is the only practical and optimal system for making collective decisions. All existing systems, such as one-person-one-vote, approval voting, or surveys, leave opportunities for everyone to be made happier without anyone doing worse.