Absolute zero is the theoretical temperature at which all molecular motion stops. It is defined as 0 Kelvin, which is equivalent to -273.15 degrees Celsius or -459.67 degrees Fahrenheit. At this temperature, a substance has minimal thermal energy, and its atoms are in their lowest energy state. Reaching absolute zero is impossible according to the third law of thermodynamics. However, scientists can get very close to this temperature in controlled environments, allowing them to study unique quantum phenomena. Experiments at temperatures near absolute zero have led to discoveries in fields like quantum mechanics and superconductivity.