iStacking or Cluster Management is a feature that allows a switch within it's web GUI to modify configurations of other switches within it's defined group members. But it's still considered as "many switches".
General or Hardware Stacking is a feature that logically transforms two (or more) connecting devices into a single machine. After enabling General Stacking mode, port interface orientation will change to allow management of stacked devices. The user will only require actual access to one management IP address.