The Baryon Oscillation Spectroscopic Survey (BOSS) was a part of Sloan Digital Sky Survey-III. It mapped the distance and direction of luminous red galaxies and quasars using normal redshift-based calculations. The data was used to determine the location of acoustic waves which are thought to form the density variations that result in galaxies, i.e., baryon acoustic oscillations. Areas dense in galaxies reveal a pattern of acoustic waves.
The follow-ons are SEQUELS (Sloan Extended Quasar, ELG, and LRG Survey) and then SDSS-IV's eBOSS (Extended BOSS or Extended Baryon Oscillation Spectroscopic Survey).