What is "flik"

In radio astronomy, the unit flik was coined by a group at Lockheed in Palo Alto, California as a substitute for the SI derived unit W cm sr µm, or watts divided by centimeters squared, steradians, and micrometers.

This is primarily used as a unit of spectral radiance or sterance. While it started out used only in Lockheed, many in the radio astronomy field adopted its use.