TUNEL staining is a laboratory technique used to detect apoptosis, or programmed cell death, in tissues. It works by labeling the ends of fragmented DNA, which is a hallmark of cells undergoing apoptosis. The method involves adding a special enzyme that binds to these DNA fragments, allowing researchers to visualize the dying cells under a microscope. This technique is valuable in various fields, including cancer research and neuroscience, as it helps scientists understand the mechanisms of cell death and its implications in diseases. By identifying apoptotic cells, researchers can gain insights into tissue development, disease progression, and potential therapeutic targets.