I've always thought of "fast" as referring to the back end of the waveform. It doesn't have any overhang or ringing. The initial transient is handled pretty well by most components, but only a few components can stop as quickly as they start. In electronics it's probably a factor of the power supply and with speakers the crossover and mass of the driver. If a component distorts the leading transient signal it can make for a faster overall presentation, but will lead to long term fatigue.
Language is always a little misleading when describing what we hear.
Language is always a little misleading when describing what we hear.