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IOS and Native IOS are the same thing.
Not precisely.
Years ago, chassis switches like the 5500 or 6500 series ran both Cat OS and IOS on them. Cat OS on the L2 supervisor and IOS on the L3 RSM. Cisco released a version of IOS that, at least for the 6500s, supported the L2 supervisor natively, i.e. Cat OS was no longer needed. Such an IOS was known as Native IOS. Running both Cat OS and IOS was known as running in hybrid mode. When both IOSs were available, you might stay with the hybrid combination as there was not 100% parity in features.
PS:
And for a bit of trivia, for the 5500s, you could also run the switch without a RSM, but working in conjunction with an external router, the later supporting MLS on the 5500.
