This equation calculates the angular frequency of a simple pendulum with a small amplitude.

This comes from the equation ω=SQRT(k/m) when k = mg/L. After substituting this in, we get the resulting equation of ω=SQRT(g/L)

References

Young, Hugh and Freeman, Roger.  University Physics With Modern Physics.  Addison-Wesley, 2008. 12th Edition, (ISBN-13: 978-0321500625 ISBN-10: 0321500628 ) Pg 437, eq 13.32