Expansion slots
From The Glossary of Digital Photography
Slots in a computer that allow the user to add additional features. For example, an expansion card can be added to allow external hard drives in a stacked enclosure to be connected to the computer. That card is known as an eSATA card. Such features are important to digital photographers with growing quantities of digital images that have to be stored. Another option would be to add another video card so that the computer could use two monitors at the same time.
