What is a "rear lift truss"?

I'm currently working on (re)certifying a German UL plane as an LSA
for the US market, and in the ASTM regulations I stumbled across:

"CS 23.369 Rear lift truss
(a) If a rear lift truss is used, it must be
designed for conditions of reversed airflow at a
design speed of –
V = 8·7 W/S + 8·7(knots)
where W/S = wing loading at design
maximum take-off weight (lb/ft2).
(b) Either aerodynamic data for the
particular wing section used, or a value of CL
equalling -0·8 with a chordwise distribution that
is triangular between a peak at the trailing edge
and zero at the leading edge, must be used."

This is from the CS 23, but the wording is the same in the ASTM-LSA
regulations.

What is a rear lift truss?

Oliver