A precise microscopic test in which samples from various body fluids (such as pleural, peritoneal, pericardial, joint, or cerebrospinal fluid) or smears from different lesions are prepared, processed, stained, and examined microscopically by a pathologist. The goal is to assess cellular characteristics, detect the presence of abnormal cells (especially malignant cells), inflammatory cells, or infectious organisms, helping to determine the underlying cause of fluid accumulation or diagnostic confusion.