The 2 Day/2 Park ticket (originally known as "bounce back") will save you $5 as opposed to purchasing two 1 day/1 park tickets. BTW, most ticket CM's won't have a clue what you are talking about if you ask for "bounce back" ticket. Ask for the 2 Day/2 Park or the 3 Day/3 Park ticket instead.
You may use the days at any park you desire but you may only do one park per day.