E_6 is a complex mathematical structure known as a Lie group, specifically one of the five exceptional simple Lie groups. It plays a significant role in various areas of mathematics and theoretical physics, particularly in the study of symmetries and particle physics. E_6 has a rich algebraic structure and is associated with a 78-dimensional representation. In addition to its mathematical significance, E_6 is also relevant in string theory and grand unified theories in physics. It is often linked to the unification of forces and particles, providing insights into the fundamental nature of the universe. Related concepts include Lie algebras and symmetry groups.