The STFT is the practical implementation of Fourier analysis for real-world signals. It divides the signal into short overlapping windows (typically 10–50ms), performs FFT on each window, and assembles the results into a spectrogram. This reveals how frequency content changes over time — essential for understanding speech, music, and transient behavior.
STFT parameters: window size (larger = better frequency resolution, worse time resolution), window type (Hann, Hamming, Blackman — different trade-offs of spectral leakage vs main lobe width), and overlap (higher overlap = smoother time evolution). The uncertainty principle means you cannot have perfect time AND frequency resolution simultaneously.