A spoonie is someone living with a chronic illness.
It mostly refers to physical chronic illnesses, though it has been known to be a helpful term for those with chronic mental illness as well.
It originates from Christine Miserandino's Spoon Theory story, in which she explains [what it's like] to live with chronic illness to a friend, and uses a handful of [spoons] to demonstrate.
For example, daily activities that healthy people tend not to think about take tolls on people with chronic illness. You start the day with a certain number of spoons, and play your day around not running out. [Socializing] might cost spoons, using the stairs might cost spoons, lifting things might cost spoons, etc.