SPIDERS: An Overview of The Largest Catalogue of Spectroscopically
  Confirmed X-ray Galaxy Clusters
  SPIDERS is the spectroscopic follow-up effort of the Sloan Digital Sky Survey
IV (SDSS-IV) project for the identification of X-ray selected galaxy clusters.
We present our catalogue of 2740 visually inspected galaxy clusters as a part
of the SDSS Data Release 16 (DR16). Here we detail the target selection, our
methods for validation of the candidate clusters, performance of the survey,
the construction of the final sample, and a full description of what is found
in the catalogue. Of the sample, the median number of members per cluster is
approximately 10, with 818 having 15 or greater. We find that we are capable of
validating over 99% of clusters when 5 redshifts are obtained below $z<0.3$ and
when 9 redshifts are obtained above $z>0.3$. We discuss the improvements of
this catalogue's identification of cluster using 33,340 redshifts, with $\Delta
z_{\rm{phot}} / \Delta z_{\rm{spec}} \sim 100$, over other photometric and
spectroscopic surveys, as well as present an update to previous ($\sigma -
L_{X}$) and ($\sigma - \lambda$) relations. Finally, we present our
cosmological constraints derived using the velocity dispersion function.
