I've been working off and on, on a desktop calendar program. It's got a number of little features one would expect from a calendar app, such as reminder/alarm, ability to add appointments, etc. It's got other little features, such as wallpaper changing (hourly, daily, weekly; random, in order, etc) and other things (shutdown/restart/hibernate windows at a specific date/time; day facts (interesting trivia); ability to always stay below (sink) under other windows and icons on the desktop).

  Anyway, I'm not a calendar person. I'm writing this for fun and it's becoming rather useful for me. So I'm thinking of making it available to everyone. But I have some questions on terminology.

  What do you call those blank days on a calendar which belong to the previous or next month. If you look at a paper calendar you'll see the days of the current month as little squares. But there are some squares that are not of the current month, but indicate a placement for the previous or next month day. What are these called?
 
Here's an image to help illustrate what I mean. The orange boxes are highlighting the areas of question.

As someone who has actually created calendars in MS Publisher for a local charity I can't say I've ever come across such a term....unless 'EMPTY BOXES' qualifies.......You could probably win WHO WANTS TO BE A MILLIONARE with this one!

I've heard it referred to as pad or padding, for instance in WordPress CSS class codes. And myself, I think of them as filler boxes.