The depth of a vertex 
in a rooted tree as the number of edges from 
to the root
vertex.
A function to return the depth of a vertex 
in a tree 
may be implemented in a future version of the Wolfram
Language as VertexDepth[g, v].
Vertex Depth
See also
Root Vertex, Rooted Tree, Tree, Tree HeightExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Vertex Depth." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/VertexDepth.html