It’s a pineapple non-dairy soft serve made by Dole that is almost exclusively available at the Disney theme parks (only a handful of other places sell it). It’s the consistency of a frozen yogurt, but since it’s not as creamy, the citrus flavor is “brighter”. It’s really, really good and since it’s mostly a Disney-only type of treat, people look forward to getting them at the parks and the line at the Dole Whip stand is routinely 30+ minutes long, year-round.
You can get it two ways: just the soft serve or as a float, which is made with fresh pineapple juice.
It really is such a gigantic deal to Disneyphiles that a couple of years ago there was a big Disneyland contest where the grand prize was a bag of the mix to make Dole Whip.