I have an analogy for what is a SinglePageApplication.

Think browser as a highly tuned racing horse. With decades of expertiese, professionals have developed methods to make it fast and efficient. It'll take you where ever you want.

SPA on the other hand is a weird looking creature.

It's made of a donkey, stacked with all kinds of extra stuff. Donkey is slow by nature and because of this extra payload it's now so heavy that it can barely move on it's own, so you need a heavy lorry to move it around. Because donkey is derived from a horse, it has it's built in features. If you give it a carrot, it will refresh it self. You don't like horsies and it's not allowed to be horse-like so you have to build obstacles to counter these features.

Now after all this pain and not gaining anything, you have an SPA and you can fantasie that it has superpowers and it can do what ever you want. If you put flame stickers on it, you can even pretend that it's a go-cart.