Signal theory

Signal theory provides a set of special mathematical approaches for use in a wide range of applications. High-level perceptions include: Amplitude, phase, resonance, Q (Q for "quality", means the strength of a resonance), time constant (of a filter), great-signal and small-signal bandwidth, maximum output swing, noise floor. Low-level perceptions include the whole spectrum of mathematics, for example integrals and differentials. If you incidentally are in statistical physics or op-amp electronics you are common with this stuff.