• When the user presses the enter or return keys while the cursor is in a text field, an event is generated.
• The Event object, named event, that is passed to the action method contains several pieces of information.
• The target field of the Event object refers to the GUI object in which the event was generated.
• input2 also refers to an object.
• The condition of the if statement tests to see if they refer to the same thing.

if ( event.target == input2 )

The condition asks: "is the target of the event the input2 text field?"

That is, did the user press enter or return while the cursor was in the input2 text field?