Simple Pendulum / Rotational Kinematics

I was just wondering where this comes from. Our professor was giving a lesson on the simple pendulum in the lab class. I copied all of the equations and how he manipulated then I understood, except for this part. I forgot to ask after class, but if you can explain it or want more relative info, let me know. Thanks so much! =)

ω2=g/L

Where ω is the rotational velocity (or speed...I don't know which is the correct way to say this), g is the gravitational force and L is the length of the pendulum.

Thanks.