Cellulitis means inflammation of the soft tissues, often due to infection.
Periorbital cellulitis is an infection of the skin around the eye. Typically, it is different from blepharitis which is an infection of just the eyelid.
Most often, periorbital cellulitis follows a cold, sinus infection, an eye infection such as a chalazion or stye, an infection of the tear drainage channels, or injury or recent surgery near the eye.
It differs from orbital cellulitis which is an infection affecting the fat and muscles within the orbit, typically lying deep to the orbital septum and most often due to underlying bacterial sinusitis.