M.2 - Wikipedia
https://en.wikipedia.org/wiki/M.2
M.2, formerly known as the Next Generation Form Factor (NGFF), is a specification for internally mounted computer expansion cards and associated connectors. M.2 replaces the mSATA standard, which uses the PCI Express Mini Card physical card layout and connectors.
M.2 Interface, Key and Socket explained
https://www.atpinc.com/blog/what-is-m.2-M-B-BM-key-socket-3
The M.2 form factor was borne out of the need for multiple options for small form factor cards, including SSDs in M.2 SSDs support both SATA and PCIe interfaces. The SATA revision 3.2 specification, in...
Understanding M.2, the interface that will speed up your... | Ars Technica
https://arstechnica.com/gadgets/2015/02/understanding-m-2-the-interface-that-will-speed-up-your-next-ssd/
Pictured at the top of this article are four different M.2 cards. The one on the left is a combo Wi-Fi The different connectors signify different M.2 "module keys." Each key exposes a different set of interfaces...