Final answer:
Marie Curie, along with her husband Pierre Curie, first coined the term 'radioactivity' to describe the spontaneous emission of radiation by uranium salts, a discovery that led to advancements in understanding nuclear decay.
Step-by-step explanation:
The term radioactivity was first coined by Marie Curie after the phenomenon was discovered by Henri Becquerel in 1896. Curie, along with her husband Pierre, conducted extensive research on uranium salts and discovered that these compounds emitted radiation, which they termed radioactivity, signifying the spontaneous emission of radiation in the form of particles or high energy photons from a nuclear reaction.
Their pioneering work, along with the contributions of other scientists like Ernest Rutherford, who investigated and named the three most common types of radiation: alpha, beta, and gamma rays, laid the foundation for the understanding of nuclear decay and radioactivity.