Non-Volatile Memory Express, also known as NVMe, is a device specification introduced by Intel in 2007. It standardizes the way that non-volatile memory devices, such as SSDs, can connect to a computer's PCI Express (PCIe) bus.
Traditionally, SSDs are connected to the computer using a disk drive interface, such as SATA. However, SATA was designed for older data storage devices, such as HDDs (hard disk drives), and its data transfer speed is limited. Beginning in about 2005, when SSDs first became popular with consumers, the fastest SSDs were reading data quicker than SATA could transfer it. Manufacturers began producing SSDs that could be installed in a PCIe slot, but their interfaces varied widely. The NVMe standard allows any of these devices to be attached to a computer without requiring separate, and possibly conflicting, operating system device drivers.
The photo shows an Intel P3608 SSD, which uses a PCI NVMe 3.0 8x interface.