Static segments aggregate subscribers at the time of creation and do not update after the segment has been created.
Dynamic segments are regenerated daily and update frequently. As additional subscribers match the criteria, they will be added to the segment, or if they no longer meet the requirements, they will be removed.
For more insights on how to create and benefit from beehiiv's segmentation tool, we've created a small series of videos to help!
Intro to Segmentation Part 1
Intro to Segmentation Part 2
Create Segment from List Upload
Segmentation with Custom Fields