This chapter introduces several typical types of aperiodic signals, including aperiodic binary signals, aperiodic M-ary signals, various frequency-modulated signals, and aperiodic pulse signals. The aperiodic resonance induced by these signals in different nonlinear systems will be investigated in this monograph. The signals presented in this chapter are simulated signals, with subsequent chapters addressing the practical engineering applications of these signal types and their corresponding experimental counterparts. Aperiodic resonance is characterized by specific indices, such as the cross-correlation coefficient, the spectral amplification factor, the bit error rate, and the logical success probability. This chapter provides a detailed introduction to these indices.