Double-stranded RNA (dsRNA) is a type of RNA molecule that consists of two complementary strands of nucleotides running in opposite directions. There are several synonyms for the term, including duplex RNA, dsRNA, and RNA duplex. Other related terms include RNA interference (RNAi), a natural phenomenon that is used to regulate gene expression, and small interfering RNA (siRNA), a type of RNA molecule that is used to silence specific genes. Additionally, dsRNA is often involved in viral replication and immune responses, and is therefore of great interest to researchers studying the molecular mechanisms of viruses and immune systems.