RNA interference (RNAi) is a process that occurs in living cells where the expression of certain genes is suppressed or inhibited by the introduction of small interfering RNA (siRNA) molecules. RNAi acts as a natural defense mechanism against foreign genetic material, such as viruses, and can also be used to regulate gene expression. The siRNA molecules bind to and degrade mRNA, preventing it from being translated into a protein. This process of gene silencing is widely used in the study of gene function and has the potential to be used in the development of new therapeutic treatments.