VarianceEstimatorFunction is an option for LinearModelFit and NonlinearModelFit which specifies the variance estimator to use.

VectorQ[expr] gives True if expr is a list or a one-dimensional SparseArray object, none of whose elements are themselves lists, and gives False otherwise. VectorQ[expr, ...

VectorScale is an option to VectorPlot, ListVectorPlot, and related functions that determines the length and arrowhead size of field vectors that are drawn.

VectorStyle is an option to VectorPlot, ListVectorPlot, and related functions that determines the style to use for drawing field vectors.

VertexColors is an option for graphics primitives which specifies the colors to assign to vertices.

VertexCoordinateRules is an option for GraphPlot and related functions which specifies rules for determining the coordinates at which vertices should be placed.

VertexCoordinates is an option to Graph and related functions that specifies the coordinates to use to place the center of vertices.

VertexCount[g] gives a count of the number of vertices in the graph g.VertexCount[g, patt] gives a count of the number of vertices that match the pattern patt.

VertexCoverQ[g, vlist] yields True if the vertex list vlist is a vertex cover of the graph g, and False otherwise.

VertexList[g] gives the list of vertices for the graph g.VertexList[g, patt] gives a list of vertices that match the pattern patt.