What is "so-dimm"

An SO-DIMM, SODIMM, or small outline dual in-line memory module, is a type of computer memory built using integrated circuits. SO-DIMMs are a smaller alternative to a DIMM, being roughly half the size of regular DIMMs.

SO-DIMMs are often used in systems that have limited space, which include notebooks, small-footprint personal computers such as those based on Mini-ITX motherboards, high-end upgradable office printers, and networking hardware such as routers and NAS devices.