A Collection is a virtual grouping of photos or videos, while a Collection Set is a folder that organizes multiple Collections and other output items like prints or web galleries. The key difference is that Collection Sets are containers for other collections, providing a higher level of organization, whereas Collections hold the actual photos. You can create Collection Sets inside other Collection Sets to build a hierarchical structure.
Collections are virtual groupings of photos that don't move the files from their original location, making them a flexible way to manage your workflow. You can also create automated "smart collections" that update automatically based on criteria you set
Working with smart collections.
Create a smart collection: Click the plus icon (+) next to "Collections" and select "Create Smart Collection".
Set criteria: Choose rules to automatically add photos to the collection, such as by rating, camera type, or date. For example, you could create a smart collection for all photos with a rating of 4 stars or higher from 2023.
See results instantly: The smart collection will automatically populate with all the photos that match your criteria
Organize collections: Create "collection sets" (folders) by clicking the plus icon and choosing "Create Collection Set." You can then drag and drop your collections into these sets.
Key concepts.
Collections vs. folders: Collections are virtual albums that group photos from different folders. They do not duplicate files on your hard drive, making them a non-destructive way to organize your work.
Quick Collection: A temporary holding area for photos you want to quickly group. You can save a Quick Collection as a new, permanent collection at any time.
Target collection: A specific collection that you can add photos to quickly by using the B key, without having to drag and drop them.
Why use collections in Lightroom Classic?
So you can have the same photo of a cat in 10 different collections. It doesn't matter to Lightroom you can put that photo into every collection or just one collection or no collections.
Should I use collections or folders in Lightroom?
Collections are different than folders. They can contain photos from many folders. They are simply a list of photos, which LR can use for specific tasks. The only time I use collections is to produce things like slideshows or photo books or similar
To rename a Lightroom Classic catalog, first quit Lightroom and locate the catalog folder, then rename the main .lrcat file and its associated .lrdata files (like Lightroom Catalog Previews.lrdata) to the same new name. Finally, open Lightroom and use the File > Open Recent > Choose a Different Catalog menu to navigate to and select the newly renamed catalog file.