A final enjoyment of freedom. For example, He's planning to have one last fling before joining the army. This expression employs fling in the sense of “a brief period of indulging one's impulses,” a usage dating from the first half of the 1800s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.