Just so you know, this is a space for rambles, but I am in no way a technician, I just like to draw :)
What is a pixel?
Here is me, basically trying to grasp some ideas based on wikipedia and resources online :D
What even is a pixel? Well, depends on the sort of screen you have, basically. We all know that modern LCD pixels are usually in a square shape, and a bunch of these squares create an image. It's a bit more complicated than that, since it's actually made of red, green and blue rectangles, but for the sake of keeping it simplified, it works.
In terms of retro aesthetics, we tend to think of CRT screens, though; where the pixels are pretty much made by electron guns. That means they are more similar to blurry dots, if anything, not quite squares.
The low refresh rate can additionally cause that screen to flicker, and the row of the electron guns - scanlines - show to the naked eye. These aspects were what often gave the retro graphics an unique, a bit blurry look. But the designers often used it to their advantage. Look at this example with the old Castlevania.
Obviously, it all also depended on the type of monitor you used. A lot of them, even in the early graphics era, were free of these effects, producing a quite clear image. Still, it can be kind of ironic how nowadays we almost never see anything resembling this effect - we prefer the square blocky pixels look without any blur or artifacts. But some games do emulate this look; for example Sonic Mania:
There is also RetroArch - a frontend for emulators - that is known for build-in shaders that emulate that look as well. It seems like a good compromise - keeping the possibility of having a clear or a blurry image depending on the user's preferences.
One more aspect I haven't see much in retro gaming scenes - some old monitors were not quite based on pixels at all, but on vectors. At the time, it helped to obtain a clearer image, but with bigger limitations on what could be drawn as well. You can see it in some of the 70s arcade games, especially space shooters, and later on, a home console called Vectrex was even released. I can understand why it's something not many people want to see in the modern era - these vector games looked weird and wonky, but I found them important to mention anyway :D
Star Wars game!
Sources:
Wikipedia, obviously.
This blog I found CRT pixels on Twitter Until next time.