The lightning talk session is an open space for people to present short talks on specific subjects. Anybody is welcome to submit a lightning talk on the day of the conference. The available time slot (one hour) will be divided evenly to allocate time for each presentation. Typically, the available time is 5 minutes.
For a discussion on why lightning talk are great, you can refer to the 2003 Perl conference: http://perl.plover.com/lt/osc2003/lightning-talks.html