FullDefinition[symbol] prints as the definitions given for symbol, and all symbols on which these depend.
FullDefinition has attribute HoldAll.
FullDefinition[symbol] recursively prints as all definitions for the symbol, and for the symbols that appear in these definitions.
FullDefinition does not look at rules associated with symbols that have attribute ReadProtected, and does not look at either rules or attributes associated with symbols that have attribute Protected.
See The Mathematica Book: Section 2.11.1.
See also: Definition, Save, Information.