  We report the discovery of six ultra-faint Milky Way satellites discovered
through matched-filter searches conducted using Dark Energy Camera (DECam) data
processed as part of the second data release of the DECam Local Volume
Exploration (DELVE) survey. Leveraging deep Gemini/GMOS-N imaging (for four
candidates) as well as follow-up DECam imaging (for two candidates), we
characterize the morphologies and stellar populations of these systems. We find
that these candidates all share faint absolute magnitudes ($M_{V} \geq -3.2$
mag) and old, metal-poor stellar populations ($\tau > 10$ Gyr, [Fe/H] $< -1.4$
dex). Three of these systems are more extended ($r_{1/2} > 15$ pc), while the
other three are compact ($r_{1/2} < 10$ pc). From these properties, we infer
that the former three systems (Bo\"{o}tes V, Leo Minor I, and Virgo II) are
consistent with ultra-faint dwarf galaxy classifications, whereas the latter
three (DELVE 3, DELVE 4, and DELVE 5) are likely ultra-faint star clusters.
Using data from the Gaia satellite, we confidently measure the proper motion of
Bo\"{o}tes V, Leo Minor I, and DELVE 4, and tentatively detect a proper motion
signal from DELVE 3 and DELVE 5; no signal is detected for Virgo II. We use
these measurements to explore possible associations between the
newly-discovered systems and the Sagittarius dwarf spheroidal, the Magellanic
Clouds, and the Vast Polar Structure, finding several plausible associations.
Our results offer a preview of the numerous ultra-faint stellar systems that
will soon be discovered by the Vera C. Rubin Observatory and highlight the
challenges of classifying the faintest stellar systems.
