A chalazion is a chronic, granulomatous inflammation of the Meibomian gland.
The Meibomian glands are sebaceous glands located in the tarsal plate of the eyelids.
Blockage of their duct leads to retained secretions, which cause a painless, firm swelling inside the eyelid.
It does not involve the glands of Zies or Moll, nor is it generalized lid margin inflammation.
Therefore, the correct answer is C only.