'T-vertices' is a term used in computer graphics

Computer graphics

Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....

 to describe a problem that can occur during mesh refinement

Subdivision surface

A subdivision surface, in the field of 3D computer graphics, is a method of representing a smooth surface via the specification of a coarser piecewise linear polygon mesh...

 or mesh simplification. The most common case occurs in naive implementations of continuous level of detail

Level of detail

In computer graphics, accounting for level of detail involves decreasing the complexity of a 3D object representation as it moves away from the viewer or according other metrics such as object importance, eye-space speed or position....

, where a finer-level mesh is 'sewn' together with a coarser-level mesh by simply aligning the finer-vertices on the edges of the course polygons. The result is a continuous mesh, however due to the nature of the z-buffer and certain lighting algorithms such as gouraud shading

Gouraud shading

Gouraud shading, named after Henri Gouraud, is an interpolation method used in computer graphics to produce continuous shading of surfaces represented by polygon meshes...

, visual artifacts

Digital artifact

A digital artifact is any undesired alteration in data introduced in a digital process by an involved technique and/or technology.-Possible causes:...

can often be detected.