“Ephemeral” is used in the sciences to refer to
short-lasting plants, animals, ecological systems, and phenomena.
It can also be used as slang to describe
people, usually in a positive sense.
An ephemeral
person is someone who wastes no time in poor relationships or situations.
For example, an ephemeral
person would not keep running back to an
ex, and an ephemeral
person would not hesitate to cut contact with someone who says or does something offensive or wrong.
An ephemeral
person could also be someone who navigates many relationships or situations in general. In this case, it is used more neutrally.
For example, to an ephemeral
person, it probably won’t matter whether you give them your number, or make out with them, or hook up with them. The end result is the same—they’re gone the next day. You’re going to have to run into them more than once for them to remember you, and really click with them to build up and maintain a friendship.
It doesn’t really translate negatively. For example, I wouldn’t call my uncle who has divorced six times too ephemeral, because an ephemeral person wouldn’t have bothered to marry anyone incompatible in the first place, let alone six times. He’s just an unreliable idiot.