Both require your permission, but there is an important difference.

With Basic Auth, you provide your username and password for the app to access Twitter, and the application has to store and send this information over the Internet each time you use the app. With OAuth, this isnt the case. Instead, you approve an application to access Twitter, and the application doesnt store your password.A lot of Twitter users are already using apps that use OAuth. Echofon, TweetDeck, Twitterrific, Seesmic, and Twitter for Android, iPhone, and Blackberry already use it.Twitter users can go to the Connections section under settings and see what all apps theyve authorized and to revoke access if necessary. If youre not using the latest versions of any apps, they may stop working because of the change.