VLANs is a grouping of ports that would make up one BCAST ( Layer 2 ) domain. They can contain one to 100's of ports (user defined). To get from one VLAN to another you need a routing (L3) function. L3 Switching term is used mostly to define a HW speed mechanism, instead of SW based forwarding used in most routers, to get a Packet routed, based on Layer 3 (IP/IPX/etc) information. MLS path, in the Catalyst switches would be the HW switching path for these packets.
Hope this clarifies,
Don