LayerSizeFunction is an option for TreePlot that gives a function to specify the relative height to allow for each layer.
LightRed represents a light red color in graphics or style specifications.
LineIndentMaxFraction is an option for Cell, StyleBox, and Style that specifies the maximum fraction of the total page width to indent at the beginnings of lines.
LinkClose[link] closes an open MathLink connection.
LocalizeVariables is an option to Manipulate that determines whether the values of variables associated with controls should be localized.
LocatorRegion is an option for Locator that specifies where the locator object should by default be allowed to go when it is dragged.
Locked
(Built-in Mathematica Symbol) Locked is an attribute that, once assigned, prevents modification of any attributes of a symbol.
MatchLocalNames is an option for Trace and related functions that specifies whether symbols such as x should match symbols with local names of the form x$nnn.
Mesh
(Built-in Mathematica Symbol) Mesh is an option for Plot3D, DensityPlot, and other plotting functions that specifies what mesh should be drawn.
MessagePacket[symbol, string] is a MathLink packet containing a Mathematica message identifier of the form symbol::string.