What is feature refinement?
Feature refinement is the step in the product management process where team and stakeholders collaborate to figure out and agree on how to build and ship a feature.
Important steps before Refinement are Discovery (where the Product Manager explores and validates different problems and solutions using an Opportunity Solution Tree) and Definition (where the Product Manager spends some time thinking on defining a feature, and expressing that in a Product Requirements Document/PRD).
The PM then goes to the team and stakeholders with the PRD in hand, to better leverage their time, with the goal of collaborating with them to refine the feature to the point where it is ready to be handed over to the development team as user stories, in e.g. in Jira.
One common practice to use in feature refinement is user story mapping.