Stitching
Computing several individual frames into one seamless spherical panorama.
Every lens sees only a section. Stitching aligns the individual frames using their overlapping areas, warps them and computes a sphere. Modern 360° cameras do part of this in-camera; better results usually come from processing on a computer afterwards.
Visible seams appear where images do not overlap cleanly — typically with subjects close to the camera. The reason is parallax: the lenses sit a few centimetres apart and see nearby objects from slightly different angles.
The best remedy is at capture time: keep enough distance from walls, furniture and people, and avoid placing the camera in tight corners.