This document classifies and defines different types of signals. It discusses analog vs digital, continuous-time vs discrete-time, periodic vs aperiodic, deterministic vs probabilistic, and energy vs power signals. Energy signals have finite energy and zero average power, while power signals have infinite energy but finite average power. The document provides examples of different signal types and calculates their energy and power. It clarifies that not all signals that approach zero as time approaches infinity are energy signals.