**Core Concept**
Non-Hodgkin's lymphoma (NHL) of the orbit is a type of extranodal lymphoma that arises in the orbital tissues. It is a malignant proliferation of lymphoid cells, often involving the lacrimal gland, conjunctiva, or orbital fat.

**Why the Correct Answer is Right**
The most common type of NHL in the orbit is MALT (Mucosa-Associated Lymphoid Tissue) lymphoma. MALT lymphomas are characterized by their association with chronic inflammation and autoimmune conditions, such as Sjögren's syndrome. The lacrimal gland is the most common site for MALT lymphomas in the orbit. These tumors often present with painless proptosis, and their treatment typically involves a combination of chemotherapy and radiotherapy.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because MALT lymphoma is the most common type of NHL in the orbit, not mantle cell lymphoma.
**Option B:** This option is incorrect because follicular lymphoma is more common in the lymph nodes, not the orbit.
**Option C:** This option is incorrect because diffuse large B-cell lymphoma can occur in the orbit, but it is not the most common type of NHL in this location.
**Option D:** This option is incorrect because Burkitt lymphoma is a highly aggressive type of NHL that is more commonly found in the jaw or abdominal lymph nodes.

**Clinical Pearl / High-Yield Fact**
MALT lymphomas in the orbit are often associated with autoimmune conditions, such as Sjögren's syndrome, and can be treated with a combination of chemotherapy and radiotherapy.

**Correct Answer:** A. MALT lymphoma