Programming

You're getting a lot of conceptual definitions, but mechanically, it's just:

keeping state (data) and behavior (functions) that operate on that state, together

At minimum, that's it. All the other things (encapsulation, message passing, inheritance, etc) are for solidifying that concept further or for extending the paradigm with features.

For example, you can express OOP semantics without OOP syntax:

foo_dict.add(key, val)  # OOP syntax

dict_add(foo_dict, key, val)  # OOP semantics

It's similar to any tech buzzword. Take "agile" for example. Agile was successfully sold as being a great idea without really being well-defined. Suddenly anyone selling a development methodology had a strong incentive to pitch it as being the real way to do agile development.

In the 90s and 2000s every 10x california tech guru agreed that OO was the future, but apparently none of them actually liked smalltalk. Instead, every new language with a hint of dynamic dispatch suddenly claimed to represent the truest virtues of OO.

There are also people who argue that smalltalk is not true OO. They say that by Alan Kay's own definition the most OO language is Erlang.

I think it's most useful to learn about that history, instead of worrying about people's post-hoc academic definitions.

OOP on its most fundamental level is the principle that stuff is represented by objects and those objects communicate with each other. That's it, that's the whole OOP.

What you are probably referring to is how OOP solves different problems and the different patterns it uses. Those are not OOP itself, those are basically instructions on how to do OOP correctly without shooting yourself in the foot.

So SOLID, IoC, dependency injection, factory, composition over inheritance and all the other famous principles are not OOP itself, but any medium-size app that's not following them is set for really fun times ~5 years down the road.

Not sure if I've answered your question, it's really vague, feel free to ask further.

Dude, you're going to shit bricks when you realize most computer science jargon is just marketing buzzwords on top of marketing buzzwords and the terms never meant anything more or less it needed to sell a product.

For example, what the hell is big data? What is a scripting language? Is your DB web scale?