Hi Kristen,
Thank you for visiting the Moms Panel with your question. I love answering dining questions:)
If you have already been to a theme park that day, then you can go to another park for your dining reservation. It will not deduct another day from the passes that you have already purchased. However, if you have not gone to a theme park that day and you're only dining at a park then a day will be deducted from your passes. Basically, you need theme park admission to get into the parks even if you're only going to a restaurant.
If you don't want to use up your park pass on just dining, there are wonderful alternatives to keep in mind. You can find incredible restaurants located throughout the Disney resorts.
Disney Springs is an amazing area, full of dining options and amazing shopping. My favorite is
Morimoto Asia at Disney Springs...if you go there you MUST try the ribs! There are so many restaurants to choose from...you may be delighted that you didn't dine in a park.
Have an amazing time at Disney Kristen!