Refine photos in Lightroom

The Refine Photos command is a tool to curate a photo collection. It works by assigning a Reject flag to those not-picked pictures and filtering the result.

This behavior enables the two-pass strategy: pick the photos you want, discard the rest. Repeat.

Flag before	Flag after
Pick	No flag
No flag	Reject
Reject	Reject

Source: Refine Photos Workflow