A vote rationale is a short written explanation of why a voter, most often a DRep, voted the way they did on a governance action. It is attached to the vote as a metadata document (following the CIP-100 governance metadata standard) and anchored on-chain, so the reasoning is permanently linked to the vote itself.
Rationales are optional but widely considered good practice: delegators choose a DRep for their judgment, and the rationale is where that judgment becomes visible. DRepTalk collects rationales and shows them on each governance action’s page alongside the vote they explain, and highlights notable ones in the activity feed.