Simply laced group

Definition
An algebraic group (or a Lie group) is said to be simply laced if its Dynkin diagram contains only simple links.

This translates to the requirement that the product of any two of the generators of the Weyl group (generators arising from a system of simple roots) has order either 1, 2, or 3.

Among the semisimple algebraic groups, the A, D, and E types are simply laced.