When you think about investments, the obvious definition refers to money. I think of an investment as something you put X in and then get more X out. I think it's more of a direct relationship to input/output.
You buy a house, you put money into it, you remodel, you build equity, etc. When you get ready to sell that house, you get your original money back plus more. Money in / Money out. Direct relationship.
When you use the word investment to refer to something else, that definition gets fuzzy. Parents will "invest" in their children's future by spending $100,000 on college. But... those parents will never see that $100,000 again. They receive non-monetary gains instead. Kids get careers, happiness, security, etc. So, you can use the word investment to refer to college, but it's not the direct input / output scenario. College is a purchase that results in value.
The same is true when talking about automobiles. You put money into a car, and you get the utility of transportation. It's not a direct relationship either. To me, that does't sound like an investment, because you put A in but you get B out. An automobile is a purchase/expense.
An investment shouldn't require anything extra to keep going. Cars consume gasoline, require insurance, tires, tune-ups, oil changes, etc. From the moment you buy a car, you never stop feeding it! That doesn't sound like an investment to me!
To review... I believe that something must have the same input/output to be considered an investment. Otherwise, it's a purchase that results in value.