**Core Concept**
Fatty liver, also known as hepatic steatosis, is a condition characterized by the accumulation of excess lipids in liver cells. This condition can result from various factors, including excessive alcohol consumption, obesity, and metabolic disorders. The primary lipid responsible for this accumulation is a type of triglyceride.

**Why the Correct Answer is Right**
Triglycerides are a type of lipid that consists of a glycerol molecule bonded to three fatty acid chains. In the context of fatty liver, triglycerides accumulate within liver cells due to an imbalance between lipid synthesis and breakdown. This imbalance can occur due to various factors, including increased fatty acid synthesis, decreased fatty acid oxidation, or impaired lipid export from the liver. The accumulation of triglycerides within liver cells can lead to liver damage and dysfunction.

**Option A:** Triglycerides are the correct answer because they are the primary lipid responsible for the accumulation in fatty liver.
**Option B:** Free fatty acids (FFA) are not the primary lipid accumulating in fatty liver. While FFA can contribute to lipid accumulation in the liver, they are not the primary cause of fatty liver.
**Option C:** Lipoproteins are involved in the transport of lipids within the bloodstream, but they are not the primary lipid accumulating in fatty liver.
**Option D:** Cholesterol is a type of lipid, but it is not the primary lipid accumulating in fatty liver.

**Clinical Pearl / High-Yield Fact**
A key feature of fatty liver is the accumulation of triglycerides within liver cells, which can lead to liver damage and dysfunction. This condition is often associated with obesity, metabolic disorders, and excessive alcohol consumption.

**✓ Correct Answer: A. Triglycerides**