In case of ANC, it definitely did things that fit the colloqual definition of terrorism - i.e. targeting civilians for political purposes:

https://en.wikipedia.org/wiki/UMkhonto_we_Sizwe#1980s:_Bombi...

That's not a justification of apartheid, though. One can argue that apartheid and terrorism are both morally despicable. Or one may argue that terrorism is sometimes justifiable.

And there are many other historical examples of the same. E.g. Soviet partisans did a lot of things that would also be considered terrorism during WW2 - targeting not Germans or their pet militias, but civilians accused of collaboratinism (which could be very vaguely defined - e.g. teachers who refused to close down schools on occupied territories). Again, you could debate whether it was justified or not, especially in the context of much broader use of terrorist tactics by Germans themselves, but that's a separate conversation.