Findability, according to an article called, The Age of Findability, by Peter Morville in Boxes and Arrows, is about designing systems that help people find what they need.

...a recent study by Vividence Research found poorly organized search results and poor information architecture design to be the two most common and serious usability problems.

In the past we haven't paid much attention to findability, but as sites get bigger, the nature of the information we're looking for gets more complex, and more interaction and our reliance on web-based information and large data systems increases, it will become more and more important to be able to quickly and accurately locate what we need.