  We present the second public data release of the Dark Energy Survey, DES DR2,
based on optical/near-infrared imaging by the Dark Energy Camera mounted on the
4-m Blanco telescope at Cerro Tololo Inter-American Observatory in Chile. DES
DR2 consists of reduced single-epoch and coadded images, a source catalog
derived from coadded images, and associated data products assembled from 6
years of DES science operations. This release includes data from the DES
wide-area survey covering ~5000 deg2 of the southern Galactic cap in five broad
photometric bands, grizY. DES DR2 has a median delivered point-spread function
full-width at half maximum of g= 1.11, r= 0.95, i= 0.88, z= 0.83, and Y= 0.90
arcsec photometric uniformity with a standard deviation of < 3 mmag with
respect to Gaia DR2 G-band, a photometric accuracy of ~10 mmag, and a median
internal astrometric precision of ~27 mas. The median coadded catalog depth for
a 1.95 arcsec diameter aperture at S/N= 10 is g= 24.7, r= 24.4, i= 23.8, z=
23.1 and Y= 21.7 mag. DES DR2 includes ~691 million distinct astronomical
objects detected in 10,169 coadded image tiles of size 0.534 deg2 produced from
76,217 single-epoch images. After a basic quality selection, benchmark galaxy
and stellar samples contain 543 million and 145 million objects, respectively.
These data are accessible through several interfaces, including interactive
image visualization tools, web-based query clients, image cutout servers and
Jupyter notebooks. DES DR2 constitutes the largest photometric data set to date
at the achieved depth and photometric precision.
