Someone of no real significance or importance in your life, who's just kind of there as part of the human population waiting to return to their nest. They could someday be important to you, but until then they are still just a randomer.
*You're opening a locker next to a randomer who is also opening his locker*
You: What's up.
Randomer: Hey, not much, you?
You: Nice, not much.
Randomer: Cool, later.
*You both leave the lockers and forget about each others' existence*