Signal Processing covers the theory, algorithms, performance analyses and applications of techniques for the processing, understanding, learning, retrieval, mining, and extraction of information from signals (1, 2)

Signal processing encompasses anything related to the manipulation of signals. In Biology signal processing is typically used for electrophysiological or imaging techniques, including, but not limited to electroencephalograms (EEG), electrocardiograms (ECG), electromyograms (EMG), single-cell recordings, magnetic resonance imaging (MRI), magnetoencephalograms (MEG) and positron emission tomography (PET). It can include techniques including, but not limited to fast Fourier transformation (FFT), wavelet analysis, determination of latency and amplitudes of neural responses, spike counting and voxel analysis.

(1): IEEE Signal Processing
(2): Wikipedia on signal processing