Hi @maulpaurer,
You can easily find default properties using the user dropdown:
Alternatively, when you export all properties via the button in the top right corner, that export will also include this information.
Regarding the question of what the difference is, you can find definitions on these pages here: HubSpot's default contact properties
You’ll find the same by searching for “hubspot company properties”, “hubspot deal properties” in your favourite search engine.
Not all of these can be deleted. Some of these default properties are provided as a courtesy, some are deeply embedded into the system.
It’s common practice to simply ignore the ones you don’t need, necessarily remove all of them.
Best regards