Governance action.
A formal on-chain proposal that, if ratified, changes protocol parameters, the constitution, or the treasury.
In depth
CIP-1694 defines several types of governance action: motion of no confidence, update to the Constitutional Committee, new constitution, hard-fork initiation, protocol-parameter update, treasury withdrawal, and a generic "info" action. Anyone can submit one by paying a deposit, which is returned later. Each action has a voting window and, except for info actions, action-specific thresholds from the governance bodies that vote on that type (DReps, SPOs, and/or the Constitutional Committee). Info actions only record votes and cannot be enacted.
Example
A treasury withdrawal of 100,000 ada to fund a public good is filed as a governance action, voted on by DReps and the Constitutional Committee (SPOs do not vote on treasury withdrawals), and only paid out once both reach their thresholds.