Design Nomenclature / Form & Geometry
G1 continuity
Also called tangent continuity, tangency, g0 continuity, positional continuity
Two curves or surfaces meet G1 when they share a point and a tangent direction there, but not necessarily curvature. The join reads as smooth in outline and in a matte render, and shows a hard kink under a specular highlight or a zebra stripe, because the reflected direction jumps. G0 below it is contact only: position, no shared tangent.
In practice
'Tangent' is the CAD word and the default a fillet gives you. Enough for a machined bracket, not enough for a Class-A surface, where a tangent-only join reads as a crease the moment a strip light crosses it.