UnderBar[expr] displays with a bar under expr.
Underlined represents an underlined font.
UndirectedGraph[g] gives an undirected graph from the directed graph g.
VerifyTestAssumptions is an option to LocationTest and similar functions that controls which assumptions to verify through diagnostic tests.
VertexSize is an option and property for Graph and related functions that specifies the size used for vertices.
White
(Built-in Mathematica Symbol) White represents the color white in graphics or style specifications.
Whitespace represents a sequence of whitespace characters in StringExpression.
WhittakerW[k, m, z] gives the Whittaker function W k, m (z).
WordBoundary represents a boundary between words for purposes of matching in StringExpression.
WordSearch is an option for Find and FindList that specifies whether the text searched for must appear as a word.