It's not an incredibly well defined concept. Anything can float or not float as you see fit (though that may require throwing a few rude gestures toward the datasheet). You can even float a 7805 on a pair of resistors like an LM317, though the current flowing out of the Ground pin may be higher and less predictable, causing a voltage drop in the resistors. Caveat engineer.
Think of it this way: I tell you Ann is five feet tall, and Bob is six feet tall. If Bob and Ann are both standing on the earth, then I know that the top of Bob's head is one foot higher than the top of Ann's. If Bob is floating in a hot air balloon, I know nothing about their relative heights (and could tether him to something and determine the height however I wanted).
Floating can refer to an entire circuit, like in the case of Bob or the LM317, or it can refer to one input, like in the case of a string tied to Bob or an unused input on a microcontroller. I can walk over and move Bob's string up and down with very little effort, though I may encounter difficulty attempting to lift it past (Bob.height + String.length) - in the same way that you cannot move a floating MCU input past roughly (VDD + 0.3).
The circuit I posted wasn't actually floating. It was a "simulated floating inductor" - within the limits of the simulation, it pretended to be a floating inductor, but it is of course still just an op amp.