A very little bit of group theory
One simple example of a group, are the symmetries of a triangle. You can rotate the triangle, or flip it. This is called a discrete group.
Another simple group is the symmetries of the circle. This is a continuous group and is called U(1)
The group SU(2) is basically the group of rotations of 3 dimensional space. The group SU(3) is more challenging to describe.
COSMOS to HUMANITY, Spring 2008
Lecture 2 , slide 21