Two planets are positioned at or very near the same degree. This is the strongest aspect. The energies of the two planets fuse together, making it difficult to distinguish one from the other. Highly intense; it can be positive or challenging depending on which planets are involved.
The astronomy in these guides is computed, not copied: sign boundaries, aspect angles and planetary positions are calculated on StarBind's own servers from the same JPL planetary data NASA uses, accurate to fractions of an arcsecond.