**Core Concept**
Fine Needle Aspiration Biopsy (FNAB) is a diagnostic procedure that involves the use of a thin needle to collect a sample of cells or tissue from a suspicious lesion. This procedure is typically used to differentiate between benign and malignant conditions, and to guide further management. FNAB is a minimally invasive technique that provides a rapid and cost-effective means of obtaining a cytological diagnosis.

**Why the Correct Answer is Right**
The correct answer is **C. Thyroid nodules**. FNAB is commonly used to diagnose thyroid nodules, particularly those that are palpable or visible on imaging studies. The procedure involves inserting a fine needle into the nodule and aspirating a sample of cells, which are then examined under a microscope for evidence of malignancy. FNAB has a high sensitivity and specificity for detecting thyroid cancer, making it a valuable tool in the diagnosis and management of thyroid nodules.

**Why Each Wrong Option is Incorrect**
**Option A:** Skin lesions. While FNAB can be used to diagnose skin lesions, it is not the most common indication for this procedure. Other methods, such as punch biopsy or excisional biopsy, may be more appropriate for skin lesions.
**Option B:** Liver masses. FNAB can be used to diagnose liver masses, but it is not the preferred method due to the risk of bleeding and the need for more definitive tissue diagnosis.
**Option D:** Pancreatic lesions. FNAB is not typically used to diagnose pancreatic lesions, as the pancreas is a retroperitoneal organ and FNAB may not be feasible or safe in this location.

**Clinical Pearl / High-Yield Fact**
FNAB is a useful diagnostic tool for thyroid nodules, but it is essential to note that a benign result on FNAB does not guarantee that the nodule is non-malignant. Therefore, follow-up imaging and clinical evaluation are often necessary to determine the final diagnosis.

**Correct Answer: C. Thyroid nodules**