Boxes are the underlying representation of two-dimensional forms in notebooks.
Boxes are the underlying low-level representation of two-dimensional formatted expressions in notebooks. Boxes can be encoded in terms of Mathematica expressions or in a more compact way as strings. Expressions can be converted to/from their box forms using ToBoxes and ToExpression. MakeBoxes defines how an expression will be converted to boxes for display by the front end.
Questions about the general typesetting capabilities of Mathematica should use the tag formatting.
Useful links:
Example questions:
