AprilTags are visual target markers (comparable to QR codes) that help with the automatic alignment of cameras or autonomous mobile robots, for example. Special AprilTag recognition software calculates the exact 3D position and alignment, which is then used for orientation. The rough black-and-white patterns are also recognizable from long distances.
In robotics, they enable fast, cost-effective, and accurate localization and orientation. This also makes them the ideal alternative in environments where GPS or other navigation aids do not work reliably.