In nuclear physics, the term "half-life" refers to the amount of time it takes for half of the nuclei in a sample of a radioactive substance to decay into another form. This concept is crucial for understanding radioactive decay, which is the process through which unstable atoms release energy and particles. The half-life is unique for each radioactive isotope and can range from fractions of a second to billions of years. It is an essential measurement for applications in radiometric dating and nuclear medicine.