1. In chemistry, "Si" is the chemical symbol of elemental silicon. Silicon is a chemical element, belonging to the metal element of group IVA in the third period of the periodic table of elements.
2. In radio and television terminology, "Si" describes data such as transmission system, transmission content and broadcast data flow schedule, which helps IRD to automatically tune and provide users with additional information so that IRD can automatically set optional services.
3. In the international system of units, "Si" is the symbol of the international system of units, which is used to represent the basic unit in the international system of units.
4. In other fields, "Si" may mean "supplier of system integration" and "integrator".
5. In Spanish, "Si" is a common word, usually translated as "yes", which is used to form a question to express surprise and translated as "but".