RegionUnion

RegionUnion[reg1, reg2, ...] gives the union of the regions.

Examples

Union of disks:

RegionUnion[Disk[{0, 0}, 1], Disk[{1, 0}, 1]]

Union of rectangles:

RegionUnion[Rectangle[{0, 0}, {1, 1}], Rectangle[{0.5, 0.5}, {1.5, 1.5}]]

Please visit the official Wolfram Language Reference for more details.