CellContext is an option for Cell which specifies the context to use for the evaluation of the contents of the cell.
Context
(Built-in Mathematica Symbol) Context[] gives the current context. Context[symbol] gives the context in which a symbol appears.
DialogProlog is an option for Dialog that can give an expression to evaluate before the dialog starts.
IntervalUnion[interval_1, interval_2, ...] gives the interval representing the set of all points in any of the interval_i.
OverscriptBox[x, y] is the low-level box representation for OverscriptBox[x, y] in notebook expressions.
ScalingMatrix[{s_x, s_y, ...}] gives the matrix corresponding to scaling by a factor s_i along each coordinate axis.ScalingMatrix[s, v] gives the matrix corresponding to ...
XMLObject["type"] represents the head of an XML object in symbolic XML.
$MachineType is a string giving the general type of computer on which Mathematica is being run.
$ProcessorType is a string giving the architecture of the processor on which Mathematica is being run.
$SystemCharacterEncoding gives the default raw character encoding for the computer system on which Mathematica is being run.