A thermal indicator is a device or material that visually shows changes in temperature. It often changes color or displays a specific pattern when exposed to different heat levels. These indicators are commonly used in various applications, including food safety, medical devices, and industrial processes, to ensure that items are kept within safe temperature ranges. Thermal indicators can be found in products like temperature-sensitive labels and thermochromic inks. They help users quickly assess whether an item has been exposed to excessive heat or cold, providing a simple and effective way to monitor temperature conditions without the need for complex instruments.