Passers by

[Rihanna]

People who you have had some kind of interaction with that have come and gone from the scope of being regularly in touch with or in touch with at all.

Persons who have briefly impacted you in some way and are no longer around.

Persons who have impacted you in a good way but are no longer around because they have continued on a path that is separate from yours. The split is usually on good terms, but you probably wont see or hear from these people again.