A paradigm is a bandwagon.

Thus a paradigm shift is changing bandwagons. Either literally hopping from one to another or burning the old one down.

It's both! Marketing blabber and general public usage have obliterated any meaning, let alone its original one.

But in the philosophy of science, Thomas Kuhn was onto something...

https://en.wikipedia.org/wiki/The_Structure_of_Scientific_Revolutions

He noted that scientific progress tends to be incremental, building and evolving what came before it. But there comes a time where what we thought we knew becomes incompatible with what we are now learning, forcing a paragigm shift.

E.g. Relativity replacing newtonian physics, or copernican heliocentrism replacing ptolemaic cosmology.

Edit: Very real. Impossible to predict. You only know after you had it.

Yes, that's more or less marketer-ese and a bullshit phrase at this point. In everyday usage it pretty much means "any change that we'd like to present as a major one", and there are ways of phrasing that so you don't sound like an advertising executive

They are real but rare. Situations that change society as a whole. For example creation of printing press which spread both religion and literacy. Or creation of the combustion engine which lead to cars and trains resulting in the society spawl we now live in. Or the discovery of germ theory which revolutionized medicine. Or the the west India shipping company started selling rights to some of the profits of a shop if people gave them money early so they could afford the ship and the trip, effectively creating stock markets(especially the futures market). Or creation of the transistor instead of vacuum tubes.

People claim things are paradigm shifts so others will give them money but most typically aren't. Like 3d tvs were supposed to be a paradigm shift about 15 years ago, now when did you last even see a 3d movie or see a 3d TV for sale in a store? Vr was supposed to be a paradigm shift for games but it's still incredibly niche due to price, downsides of current tech and lack of software (software isn't developed because there's not a consumer base and there's not a consumer base because there's no software)

A sociologist named Alvin Toffler wrote a book called "Future Shock' back in the 1960s. He predicted that there was going to be a massive shift from the Industrial Age to the Digital Era. A science fiction writer named John Brunner read Toffler's book and wrote "Stand On Zanzibar" a novel about the early 21st Century.

Brunner's book has things like school shooters, legalized marijuana, AI, LGBT+ becoming mainstream, etc etc.