The changes are found in iTunes Connect, the service which is used by developers to submit content to the App Store.
Developers are informed that "It is important to enter keywords for all applications as soon as possible so your application can continue to be successfully located on the App Store."
"Keywords can be updated with the submission of a new binary."
The are over 65,000 applications available in the App Store which often makes it difficult to find the right app for your iPhone or iPod touch. The addition of keywords should provide a marked improvement in searchability.