Spliceosome is a complex macromolecular assembly that is essential for the removal of introns from eukaryotic pre-mRNA. Synonyms for spliceosome include pre-mRNA splicing factor, pre-mRNA splicing complex, and RNA splicing machine. Other terms to describe this process include RNA splicing, intron removal, and RNA processing. The spliceosome is composed of several small nuclear ribonucleoprotein particles (snRNPs) and accessory proteins, which assemble in a defined sequence to form an active splicing complex. Alternative splicing is a phenomenon where different splice sites are used to generate different mRNA isoforms, enabling eukaryotic organisms to expand their protein repertoire. The spliceosome plays a crucial role in regulating gene expression, and its dysfunction is implicated in various human diseases.