InputNamePacket[string] is a MathLink packet that contains in string the name to be assigned to the next input.
LibraryFunctionLoad[lib, fun, argtype, rettype] loads Wolfram Library lib and makes the library function fun available in Mathematica.
LimitsPositioningTokens is an option for selections that specifies a set of characters for which the option LimitsPositioning is set to True by default.
LineBreakWithin is an option for selections that specifies whether line breaks occur automatically when the end of a line is reached.
LinkConnect["name"] connects to a MathLink link created by another program.
ListPlay[{a_1, a_2, ...}] creates an object that plays as a sound whose amplitude is given by the sequence of levels a_i.
symbol::tag is a name for a message.
MinusPlus[x] displays as \[MinusPlus]x.MinusPlus[x, y, ...] displays as x \[MinusPlus] y \[MinusPlus] ....
NCache
(Built-in Mathematica Symbol) NCache[x, xn] represents a numeric cache object for a quantity with exact value x and approximate numerical value xn.
Negative[x] gives True if x is a negative number.