Thermochromism is a phenomenon where materials change color in response to temperature variations. This occurs because the molecular structure of the material alters with temperature, affecting how it absorbs and reflects light. Common examples include certain types of thermochromic inks used in products like mood rings and temperature-sensitive labels. These materials can be classified into two main types: reversible and irreversible. Reversible thermochromic materials return to their original color when the temperature changes back, while irreversible ones do not. This property has practical applications in various fields, including packaging, textiles, and thermometers.