The uranium decay series refers to a sequence of radioactive decay processes that begin with the isotope uranium-238 and end with stable isotopes, such as lead-206. As uranium-238 decays, it transforms into various intermediate isotopes, including thorium-234 and radium-226, each of which also undergoes further decay. This series is significant in understanding the behavior of radioactive materials in nature. The decay process releases radiation and can be used in applications like radiometric dating and nuclear energy. The entire series illustrates how unstable isotopes evolve over time into stable forms.