InputStream["name", n] is an object that represents an input stream for functions such as Read and Find.
IsomorphicGraphQ[g_1, g_2] yields True if the graphs g_1 and g_2 are isomorphic, and False otherwise.
LayerSizeFunction is an option for TreePlot that gives a function to specify the relative height to allow for each layer.
LCM
(Built-in Mathematica Symbol) LCM[n_1, n_2, ...] gives the least common multiple of the n_i.
LinkProtocol is an option to LinkLaunch, Install, and related functions that specifies the underlying data transport protocol to use for a new MathLink link.
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.
MathieuGroupM22[] represents the sporadic simple Mathieu group M_22.
MathieuGroupM23[] represents the sporadic simple Mathieu group M_23.
PageBreakAbove is an option for Cell which specifies whether a page break should be made immediately above the cell if the notebook that contains the cell is printed.
PageBreakBelow is an option for Cell which specifies whether a page break should be made immediately below the cell if the notebook that contains the cell is printed.