The sensor section was one or more sections on the USS Enterprise that took sensor readings.
In 2267, having lost contact with the passengers of the Galileo, Captain James T. Kirk asked for their readings on Taurus II, but they doubted the reliability of their findings due to static interference. Later, they reported their beams were functioning again.
Believing there might be a slim hope of recovery, and after deciding to head to Makus III, he ordered all sensor sections to direct their beams aft, in case the Galileo was still out there. (TOS: "The Galileo Seven")