From Facebook Developer Wiki

Feed forms allow applications to publish Feed stories on behalf of users and Pages. Feed forms let users publish application stories to their own Walls or to the stream of one of a user's friends.

You create a Feed form using one of two methods:

• Facebook.streamPublish: An FBJS call for FBML applications.
• FB.Connect.streamPublish: A JavaScript Client Library call for Facebook Connect sites, desktop applications, and IFrame applications.

To create a Feed form, you need to create an attachment that provides the data for the form, and you need to keep the auto_publish parameter set to the default, false.

For more information on creating a Feed form, read the article for the appropriate call above.