Photo albums and Smart Albums
You can make standard photo albums to collect photos of certain subjects or to temporarily group photos you plan to use in a project, such as a slideshow. Albums can contain photos taken anytime or anywhere. You can place the same photo in several different albums and organise albums in different ways.
Smart Albums are special photo albums that Photos updates for you automatically, using criteria you specify. For example, you can create a Smart Album that collects all the photos assigned a specific keyword, or a Smart Album that groups all the photos taken with a particular camera.