-Lenin mainly used terror to defend revolution against opposition. e.g. Social-Revs
-Stalin's much more widespread, used against party members, soviet people and relatives of rivals.
-Lenin sent Social Revs to labour camps as part of the Red terror.
-Stalin took this idea but scaled it up by sending millions of people to his labour camps, gulags. (Could be seen as similar)
-Both used terror for multiple uses but Stalin's was much bigger and detrimental to soviet society. this is why they're fundamentally different.