SATA Express is a computer interface which can support both SATA and PCI Express devices and is designed as a successor to SATA 3.0 enabling faster data transfers. It allows the use of existing SATA connectors, making it compatible with existing storage devices, but also allows for the use of the much faster PCI Express bus via the latest SATA Express connectors.
SATA Express increases the maximum transfer speed from 6Gb/s for SATA 3.0, to about 16Gb/s (but other factors affect it).