It simply means one cares deeply about the welfare of another.
The biggest difference between paternal, sibling, platonic, and romantic love is we usually have a desire to be (physically intimate) with our "romantic love" mate/spouse.
Having said that when it comes to romantic love everyone has their own definition or expectations. Each person has made up their mind what love is suppose to "look like", "feel like", and how people "in love" should "act like".
Ultimately we're looking for someone to love us (the way) we want to be loved! Until that happens we won't (feel loved) no matter what is in our mate's heart.
This explains why some people tell their mates: "If you loved me you would..." Essentially we want people to love us (the way) we want to be loved! The tricky part is finding someone who (naturally) expresses love (the way) one wants!
There is no "universal definition" or expression for love!