The universe in which Alice Oseman's character's live and exist in. The characters in Solitare, Radio Silence, I Was Born This Way, Nick and Charlie, This Winter, and all 4 Heartstopper books are the characters in the Osemanverse.
"Who's your favorite character in the Osemanverse?"
"Definitely Aled Last or Tori Spring!"
Osemanverse syndrome is a condition where you can't think about anything but the lovely universe that Alice Oseman created around their books. So basically you're extremely obsessed.
"you need to go to sleep! And when is the last time you had something to eat or something to drink!?"
"I don't need sleep or food and drinks I need the osemanverse!"
"What is the osemanverse?"
"the osemanverse is a universe centered around Alice Oseman's books"
"Okay, I see. I hereby diagnose you with Osemanverse syndrome"
"What is osemanverse syndrome?"
"Osemanverse syndrome is a condition where you can't think about anything but the lovely universe that Alice Oseman created around their books. So basically you're extremely obsessed."
"Oh I definitely have that"
"I know"