The Discussion topic will identify your topic in the Discussion index and will appear at the top of the discussion page. A filename will be created from the topic with characters other than numbers and letters converted to dashes and underscores. If the Discussion topic is greater than 25 characters, only the first 25 will be used for the file name. (Given these conversions, it's possible for two topics to translate into the same filename; if so you will be notified.)