This lecture introduces the concept of Parallel Prefix Adders (PPA), a systematic approach to designing optimized adder architectures. It covers various types of PPAs such as Ripple Carry Adder (RCA), Sklansky, Brent Kung, Kogge Stone, and Carry Increment Adder (CIA). The lecture explains the principles behind PPAs, including pre-processing (P and G generation) and post-processing (S generation), and discusses the performance and hardware overhead of different PPA structures.