Gapper Share definition Flag Soldiers stationed at Ft. Indiantown Gap in Pennsylvania back when it was still an army base, especially in the WWII and Korean War eras. Locals that lived in the towns near the base (mainly Lebanon, PA) called them "gappers". Gapper by Loretta Lou June 24, 2009 0 0 Get merch Get the Gapper mug. Buy Now — $32.95 See more merch