understand "extent"

Hi, The context is RBD on bluestore. I did check extent on Wiki. I see "extent" when talking about snapshot and export/import. For example, when create a snapshot, we mark extents. When there is write to marked extents, we will make a copy. I also know that user data on block device maps to objects. How "extent" and "object" are related? Can I say extent is a set of continuous objects (with default tripe settings)? Thanks! Tony