A switch virtual interface (SVI) is a virtual interface on a switch that belongs to a particular VLAN. It is a layer three interface that can be assigned an IP address.
For Layer 2 switches, an SVI is used as a destination IP to gain access to the switch's CLI management via Telnet or SSH.
For Layer 3 switches, an SVI can also act as a default gateway for the subnet assigned to that particular VLAN. Using Inter-VLAN routing, a Layer 3 switch can route traffic it receives on the SVI.