Telomere shortening refers to the gradual reduction in the length of telomeres, which are protective caps located at the ends of chromosomes. Each time a cell divides, these telomeres become shorter. This process is a natural part of cellular aging and helps prevent the replication of damaged DNA. As telomeres shorten over time, they eventually reach a critical length, leading to cellular senescence or apoptosis (programmed cell death). This phenomenon is associated with various age-related diseases, including cancer and cardiovascular diseases, as well as the overall aging process in organisms.