Definition

Definition[symbol] prints as the definitions given for a symbol.

Definition["symbol"] prints as the definitions given for the symbol named "symbol" if it exists.

Definition[patt] prints as the definitions given for the symbols whose names textually match the arbitrary string pattern patt.

Definition[{spec1,spec2,…}] prints as the definitions given for the symbols that are equal to or or whose names match any of the speci.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.