For built-in symbols, Definition gives attributes, defaults, and options:

For user-defined symbols, Definition gives attributes, defaults, options, and definitions:

For read-protected symbols, definitions are not given:

The information given by Definition is comprised of defaults, options, attributes, and values:

Information prints the values rendered by Definition, as well as usage messages:

?? is the same as Information:

Definition is HoldAll:

This gives the definition of symbol itself:

This gives the definition of its value:

Definition is an output form; it does not evaluate: