What is the difference between collections and galleries?

Collections are groups of images, just like galleries, but they are never published on your website.

They are therefore suitable for your own library management purposes, like selections for your admin space.

They can also be used to automate actions, for example automatically pricing images based on their metadata.

Unlike galleries, collections cannot be nested.

See also

Creating and using multiple media libraries ›
What are smart collections for? ›
Adding, managing and deleting websites ›
Using automation features ›
How should I organize my galleries? ›