Definition
Create a first iteration of your product with the absolute minimum set of features that would make it valuable and useful, at least to early adopters.
Example
The first version of the iPhone did not support cut-and-paste, it offered a very limited number of apps, it did not support notifications or the uber-popular Microsoft Exchange email back-end, and it required iTunes to activate/use it. But people wanted it so much that they did not care about the missing functionality, a great indicator of interest.