SU(n) is a special type of mathematical group known as a Lie group, which is important in the fields of mathematics and theoretical physics. It consists of all n x n unitary matrices with a determinant of 1. These matrices preserve the inner product in complex vector spaces, making SU(n) crucial for understanding symmetries in quantum mechanics and other areas of physics. The notation SU(n) indicates that the group is related to n dimensions. For example, SU(2) is significant in the study of spin and isospin in particle physics, while SU(3) is essential for the theory of strong interactions in quantum chromodynamics.