if you go into the Modules area, you will see "About" and "Help" for each module.
This is from there, see optional parameter 2
How do I use it?
As this is just a tag module, it's inserted into your page or template by using the cms_module tag. Example syntax would be:
{cms_module module="rss" url="
http://download.freshmeat.net/backend/fm-releases.rdf" numbertoshow="5"}
Parameters
* url="http://feed_url" - RSS feed URL
* (optional) numbertoshow="5" - Maximum number of items to display -- leaving empty will show all items.
* (optional) target="" - Adds a target param to the title link. Set to "_blank" to open in a new page.
* (optional) descriptions="1" - Show the description of the RSS articles.
* (optional) lang="en_US" - Parameter is used to specify what language to use for display on the frontend. Not all modules support or need this.