That's Walt Disney World's theme for this year. It means they will doing lots of short promotions, sometimes for a few weeks, sometimes for a few days. These can take the form of special events or celebrations or anything else they dream up. The first one starts January first and runs a couple weeks. It's a nightly New Year's Countdown dance party in Tomorrowland. It sounds fun, I'd go to it for sure if I were there, but it wouldn't make me want to plan a trip around it. This is going to be fun to watch, I think, to see what Disney comes up with throughout the year. The downside, as my friend pointed out, is that if they do something really cool, it will kill us to not be able to see it or participate. It will be kind of like Limited Time Torture for Disney Geeks.
Here's the link to the official Limited Time Magic web page, where the promos will be announced and explained. I know I'm going to be checking it out often. Even if that is torturing myself.