Collections allow you to group ProductVariants together by various criteria. A typical use of Collections is to create a hierarchical category tree which can be used in a navigation menu in your storefront.
Collections are dynamic, which means that you define a set of rules, and Vendure will automatically populate the Collection with ProductVariants according to those rules.
The rules are defined by filters. A Collection can define multiple filters, for example:
Collections can be nested inside one another, as many levels deep as needed.
When populating a nested Collection, its own filters plus the filters of all Collections above it are used to calculate the contents.
A Collection can be made private, meaning that it will not be available in the storefront. This can be useful when you need to organize your inventory for internal purposes.