When the Georgia Southern University Jazz Ensemble presents a free, public concert in the Performing Arts Center at 7:30 p.m. Monday, the show will have one thing in common with all other jazz performances: It will be unique. The one-off nature of jazz performance is a cliché, but a true one, and 2016-17 brings the ensemble's 20 or so musicians unique opportunities. A recent-past performance at the Averitt Center for the Arts and the near-future show at the PAC become prelude to another show for which tickets are already selling quickly.