Magma is an environmental feature found in the Desert biome and is exclusive to Don't Starve Together. These pools are a part of a Set Piece found in the Desert, which serves as a spawn point for the Dragonfly. They are used by the Dragonfly to spawn Lavae.
Magma is often surrounded by small rocks, much like Ponds are surrounded by Plants or Algae. The Set Piece also has burnt Spiky Trees and Spiky Bushes, Crispy Skeletons that cannot be destroyed for resources, and numerous scorch marks on the ground.
Standing too close to Magma will cause the player, mobs, and most items to catch fire. However, it should be noted that there is a slightly larger radius in which the player will take fire damage but will not be set on fire.
Magma also glows in the dark, but the pool's light radius is too small to be useful, as it doesn't reach past the "burn zone". Its heat radius is much larger than its light radius, so a player staying near one during Winter can avoid freezing. This heat radius can warm thermal stones, which can provide light outside the "burn zone" and allow a player to survive the night with no other light sources.
It is possible to overheat from standing near a magma pool even during the winter, which can be very useful to allow for more time away from a heat source.
Willow will still catch fire when in the burn range, even though she is fire resistant.
Tumbleweed on fire after bouncing across a Magma pool