Depth[expr] gives the maximum number of indices needed to specify any part of expr, plus one.
Raw objects have depth 1.
The computation of Depth does not include heads of expressions.
Depth treats SparseArray objects just like the corresponding ordinary lists.
See Section 2.1.7.
See also: ArrayDepth, Level, LeafCount, Length, Nest.
New in Version 1; modified in 5.0.