Soft forks are opt-in "updates" or "features" that are still backward compatible in regard to bitcoin's hard coded consensus rules.
They've also changed consensus rules, BIP66 changed signature validation, making it more selective. And it was an important consensus change, too.
I'm talking about new consensus change tho. From now on and as even heavily marketed segwit fork seems not to take root.
Such decentralization, much immutability ftw!