I had never heard this term before, but a quick googling got me a thread from 2006 on RC Groups.
Link if you're interested:
https://www.rcgroups.com/forums/showthread.php?489757-what-is-a-shock-flyer
User Safety Hawk summed it up with the following:
"Well, I don't mean to over define this, but the "Shock Flyer" is an actual style of plane created by
Ikarus, and it essentially started the flat plate foam trend. Somehow, now everyone seems to generalize the name "Shock Flyer" or "Shocky" for short, to mean any flat plate foam plane. It's kinda like how everyone calls hook and loop tape "Velcro." Velcro is actually a brand name.