In a Yagi-Uda antenna array, a director is a parasitic element cut slightly shorter than the active dipole. It focuses the electromagnetic field into a tighter beam, pulling the radiation pattern forward. Adding multiple directors increases the antenna's overall directivity and gain, which is why long UHF television antennas have a row of progressively shorter crossbars at the front.
Heard on the job
We lost a director in the ice storm, which explains why the signal strength dropped on the forward link.