What's the difference between saturation and distortion?

https://www.soundonsound.com/sound-advice/q-whats-difference-between-saturation-and-distortion

How do you differentiate between the following terms: saturation, harmonics, distortion, overdrive? Are all of these just similar terms with different names? When should we use one of these versus the other? Is there a way to quantify or measure the addition of these signal enhancements other than just by their sound — perhaps with something like DDMF's Plugindoctor? Do you have any good references to recommend of songs to strive to emulate? How can you tell if you've over-baked your track and gone too far?