"Radioactive" refers to the property of certain materials that emit radiation as they decay. This process occurs when unstable atomic nuclei lose energy by releasing particles or electromagnetic waves. Common radioactive elements include uranium and radium, which can be found in nature and are used in various applications, including energy production and medical treatments. Radiation can be harmful to living organisms, as it can damage cells and DNA. However, it also has beneficial uses, such as in radiotherapy for cancer treatment and in nuclear power plants for generating electricity. Understanding radioactivity is essential for safety and effective use in these fields.