What does the term "in-plane" refer to in tiling?

The term "in-plane" in tiling specifically refers to the alignment of tiles such that they all lie on the same flat surface or plane. This is crucial for achieving a visually appealing finish and ensuring that surfaces do not have uneven spots where tiles may protrude or dip. Proper alignment is essential for both aesthetics and functionality, as it prevents issues such as tripping hazards and makes cleaning easier. Ensuring that all tiles are "in-plane" helps maintain a uniform appearance across the entire tiled area, whether it’s a floor, wall, or backsplash.

The other concepts listed do not pertain to the definition of "in-plane." While the distance between tiles, thickness of the tile installation, and color variation are all important aspects of a tiling project, they do not relate to the planar alignment of tiles. Thus, focusing on the alignment ensures that the installation meets quality standards and adheres to ANSI regulations for tiling.