vlan:svi

cisco doc: ENG-32517 VLAN IP Switch Virtual Interface
vlan x is layer 2, snmp-mib descr unrouted vlan
int vlan 2 is layer 3, snmp-mib descr routed vlan (short name vl2)

Another doc: Native IOS Configuration Lab Catalyst 6500, 4500, 3550 systems
For CCIE Study and Network Simulation