Each one means different things.
A month ago in this crisis timeline, I had shared The Differences Between Quarantine and Isolation.
Now new terms have been introduced, such as "Shelter in Place." Sounds like a good description, until you have a chemical release emergency and an order to "Shelter in Place" is given, which, besides meaning stay indoors, you should shut off your HVAC system and move to an interior room in the home. The whole "duct tape and plastic" fiasco, post-9/11 is what "Shelter in Place" is about.
I do like the term "Lockdown" for telling people to stay home. It is a new term, it does not indicate you have COVID-19 which would be "self-isolate." And, it doesn't indicate that you have been exposed to the virus by another person, which "Quarantine in Place" would indicate.
I'm sure we will screw it all up somehow. If not for today, then for some future emergency. I hope they think through what term they use when the order to "Lock it Down" is given. My definition would be stay at home except for essential trips to: the grocery store, pharmacy, doctor, and work- - if you are designated an essential worker in the area of critical infrastructure.
Here is the Department of Homeland Security's critical infrastructure designations.