NVMe is a communications interface/protocol developed specially for SSDs.
Communication with mass storage has often changed. From MFM and ESDI to SCSI, P-ATA, SAS, SATA or even directly attached to the PCI-e bus. The standard used in most recent computers often was SATA. SATA is fast enough for classic harddrives but has a relative high overhead. This does not matter much for hardrives which still have to reposition their heads, which takes significant time.
Solid state storage however has no such need and the current SATA/AHCI protocol limits it needlessly.
NVMe is designed to take advantage of the new solid state drive technology, resulting in improved performance.
In oder to boot from a NVMe SSD you need firmware (e.g. BIOS or UEFI) which understands the protocol. Without this you can still use the drive as long as you have the driver for your OS, but you cannot boot from it.
