The history of an interactive Mathematica computation is both maintained in a fully editable Mathematica notebook, and is stored symbolically in a sequence of In and Out ...

AnimationDirection is an option which specifies the direction to run an animation.

Bookmarks is an option for Manipulate and related functions that gives a list of bookmark settings.

CellAutoOverwrite is an option for Cell which specifies whether an output cell should be overwritten by new output when the preceding input cell is evaluated.

GraphicsColumn[{g_1, g_2, ...}] generates a graphic in which the g_i are laid out in a column, with g_1 above g_2, etc. GraphicsColumn[list, alignment] aligns each element ...

Null is a symbol used to indicate the absence of an expression or a result. It is not displayed in ordinary output. When Null appears as a complete output expression, no ...

Skeleton[n] represents a sequence of n omitted elements in an expression printed with Short or Shallow. The standard print form for Skeleton is <<n>>.

Spacings is an option to Grid and related constructs that specifies the spacings to leave between successive objects.

WordSeparators is an option for Read, Find, and related functions that specifies the list of strings to be taken as delimiters for words.

Nearest[{elem_1, elem_2, ...}, x] gives the list of elem_i to which x is nearest. Nearest[{elem_1 -> v_1, elem_2 -> v_2, ...}, x] gives the v_i corresponding to the elem_i to ...