Stacking technology unites multiple switches into a single logical unit, using stack interconnect cables. The stack behaves as a single switching unit that is managed by a master switch elected from one of the member switches.
Cisco Switch Clustering technology is a set of software features available to all Catalyst 3500 XL, 2900 XL, 2955/2950, 2970, 3550, 3560, 3750, 4500, and Catalyst 1900/2820 Standard and Enterprise Edition switches. Switch Clustering technology allows to manage up to 16 switches, concurrently, through a single IP address
Below table enumerates the difference between Stacking and Clustering –
More detail on Switch Clustering is available via below link –