Gives the shortest distance from a point to a region. It is zero inside a solid
RegionDistance[reg, p]
RegionDistance[reg1, reg2]
RegionDistance[reg]
RegionDistance[Disk[{0, 0}, 1], {3, 0}]
→ 2RegionDistance[Point[{0, 0}], {3, 4}]
→ 5RegionDistance[Rectangle[{0, 0}, {2, 2}], {3, 3}]
→ Sqrt[2]