Small Interfering RNA (siRNA) is a class of double-stranded RNA molecules, typically 20-25 base pairs in length, that play a crucial role in the regulation of gene expression. They are involved in a process called RNA interference (RNAi), where siRNA can bind to complementary messenger RNA (mRNA) sequences, leading to the degradation of the mRNA and preventing the production of specific proteins. siRNA is widely used in research and therapeutic applications to silence genes associated with diseases. By introducing synthetic siRNA into cells, scientists can selectively inhibit the expression of target genes, making it a powerful tool for studying gene function and developing treatments for conditions like cancer and viral infections.