  Deep optical and near-infrared imaging of the entire Galactic plane is
essential for understanding our Galaxy's stars, gas, and dust. The second data
release of the DECam Plane Survey (DECaPS2) extends the five-band optical and
near-infrared survey of the southern Galactic plane to cover $6.5\%$ of the
sky, |b| < 10{\deg} and 6{\deg} > l > -124{\deg}, complementary to coverage by
Pan-STARRS1. Typical single-exposure effective depths, including crowding
effects and other complications, are 23.5, 22.6, 22.1, 21.6, and 20.8 mag in
$g$, $r$, $i$, $z$, and $Y$ bands, respectively, with around 1 arcsecond
seeing. The survey comprises 3.32 billion objects built from 34 billion
detections in 21.4 thousand exposures, totaling 260 hours open shutter time on
the Dark Energy Camera (DECam) at Cerro Tololo. The data reduction pipeline
features several improvements, including the addition of synthetic source
injection tests to validate photometric solutions across the entire survey
footprint. A convenient functional form for the detection bias in the faint
limit was derived and leveraged to characterize the photometric pipeline
performance. A new post-processing technique was applied to every detection to
de-bias and improve uncertainty estimates of the flux in the presence of
structured backgrounds, specifically targeting nebulosity. The images and
source catalogs are publicly available at http://decaps.skymaps.info/.
