MLS is Multi Layer Switching basically layer 3 switching

Cisco Quotes:

IP MLS provides high-performance hardware-based Layer 3 switching for Catalyst 5000 family and 2926G series LAN switches. IP MLS switches unicast IP data packet flows between IP subnets using advanced ASIC switching hardware, offloading processor-intensive packet routing from network routers.

for more info url is:

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_5_2/layer3/mls.htm#xtocid171391

good luck

Chris