The centroid tag specifically references plane figures. In rehabilitating this Question, "Integrating to find mass and centre of mass", I wanted to add a relevant tag to the current "calculus". However the shape there is (if interpreted simply) three-dimensional.
Given the commonality in defining a center of mass in two and three (and higher) dimensions, I propose that the "centroid" tag should include the higher dimensional cases. At the least I would change "a plane figure" in the tag-excerpt and -wiki to "a plane or solid figure".
We possibly could allow for weighted centers (nonuniform mass density), although this is strictly outside the meaning of "centroid" or "geometric center".
Another Question that asks about three-dimensional figures and how to calculate their centers of mass is Center of mass of semi-sphere. It currently has only the "integration" tag. This closely related Question (possibly a duplicate) does use the "centroid" tag without reluctance.
Update: I made the above change "... or solid" to both tag excerpt and wiki, noting the relation to center of mass when density is constant (uniform). I'll make a survey for Questions relating to center of mass calculations when density is variable, and if there are enough (ten or more) I'll create that tag.