What is a "Land And Hold Short Of" light?
It's an in-pavement (flush) light bar that indicates the hold-short for the LAHSO operations. See: What is a land and hold short clearance (LAHSO)? For the FAA they are:


  FLASHING L-850A OR L-850F LIGHT FIXTURE (Source: AC No: 150/5345-54B)


A single L-850F unit in the light bar looks like this:


(adbsafegate.com)


(FAA AIM) The light bars are located as indicated by the blue arrows.

I tried to find a video to show the pulsating white light at night when in use, but I couldn't find any. By checking Boston Logan (KBOS) on Google Earth, and zooming in at where the LAHSO hold-short lines are, the flush light fixtures can be barely seen: