The central object in FRG is a scale-dependent effective action functional Γ Γ k often called average action or flowing action. The dependence on the RG sliding scale k is introduced by adding a regulator (infrared cutoff) R k to the full inverse propagator Γ Γ k ( 2 ) . Roughly speaking, the regulator R k decouples slow modes with momenta q ≲ ≲ k by giving them a large mass, while high momentum modes are not affected. Thus, Γ Γ k includes all quantum and statistical fluctuations with momenta q ≳ ≳ k . The flowing action Γ Γ k obeys the exact functional flow equation