From the Cardano website:
The Voltaire era of Cardano will provide the final pieces required for the Cardano network to become a self-sustaining system. With the introduction of a voting and treasury system, network participants will be able to use their stake and voting rights to influence the future development of the network.
For the Cardano network to become truly decentralized, it will require not only the distributed infrastructure introduced during the Shelley era but also the capacity to be maintained and improved over time in a decentralized way. To that end, the Voltaire era will add the ability for network participants to present Cardano improvement proposals that can be voted on by stakeholders, leveraging the already existing staking and delegation process.
To fund the future development of the network, Voltaire will also see the addition of a treasury system, whereby a fraction of all transaction fees will be pooled to provide funds for development activities undertaken following the voting process.
When both a voting and treasury system are in place, Cardano will be truly decentralized and no longer under IOHK’s management. Instead, Cardano’s future will be in the hands of the community, who will have everything they need to grow and evolve Cardano from the secure, decentralized basis established by IOHK.
We’re working on more content for this era of the roadmap and will be updating this page at an appropriate time. Meanwhile, all the latest updates on technical progress are delivered as part of the Cardano Weekly Technical Reports.