eSATA is the name of the standard for external SATA. The standard is the same as for the SATA that you normally use to connect the hard disks inside the computer, but the eSATA variant gives you the option of connecting units externally, e.g. external hard disks. This means that an external hard disk can use the SATA default and its high speed rather than e.g. being connected via the slower USB standard. With this cable you can connect an eSATA unit to the eSATA port in your computer.