system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: the difference between regular, high-mileage, and synthetic motor oils.
gpt
Regular (aka conventional) is created from crude oil. It's plentiful and cheap, but loses it's lubrication properties quickly and needs to be changed often.

Synthetic oil are man-made (synthesized, hence the name) that have the properties of conventional motor oil. Advancements have allowed for synthetic oil to last much longer than regular oil, but is still quite pricey compared to the cost of regular oil.

High-mileage oils are usually a hybrid of the two or a pure synthetic (check the labels). The hybrid will be cheaper (due to mixing of the cheap conventional oil and the synthetic) and, in theory, should last longer.

Now, the question that you probably want to derive from this if using one has a benefit over the other. Usually your car will run perfectly fine on either, as they both will provide sufficient lubrication for engines for 98% of the population. Most German vehicles come with synthetic (which allows for BMW / Audi / MB to stretch oil changes to 15,000 miles) while most other vehicles come with conventional. The switch to synthetic should allow for you to stretch your oil changes further apart than with regular oil, but it will be more expensive to change the oil due to the cost of the synthetic. Your car's owners manual should have guidelines as to which oil you should be using. And despite what some people will say, switching between either shouldn't impact your vehicle if the engine is already in good shape and you're using brand new conventional oil.