**Core Concept**
A chalazion is a type of benign eyelid lump caused by a blockage of the meibomian gland, leading to inflammation and the accumulation of sebum and cellular debris. The meibomian glands are located within the tarsal plates of the eyelids and play a crucial role in the maintenance of the tear film.

**Why the Correct Answer is Right**
A chalazion typically presents as a painless, firm, and non-tender nodule on the eyelid, often accompanied by mild swelling. The blockage of the meibomian gland leads to a localized inflammatory response, which can cause the gland to become distended and eventually rupture, releasing a cheesy or oily discharge. The meibomian glands are innervated by sympathetic nerves, which may contribute to the painless nature of chalazia.

**Why Each Wrong Option is Incorrect**
**Option A:** A chalazion is not caused by a viral infection, as it is a benign lump resulting from a blockage of the meibomian gland, not an infectious process.
**Option B:** A chalazion is not typically associated with a sudden and severe onset, as the blockage of the meibomian gland is a gradual process that leads to inflammation and swelling.
**Option C:** A chalazion is not a type of malignant tumor, as it is a benign condition resulting from a blockage of the meibomian gland.

**Clinical Pearl / High-Yield Fact**
Chalazia are often confused with other types of eyelid lesions, such as styes or hordeolum, which are caused by bacterial infections. However, chalazia are typically painless and do not have a purulent discharge, whereas styes are often painful and accompanied by a thick, yellowish discharge.

**Correct Answer:** D.