In time series data such as sound, the sampling rate is the rate at which measurements are taken. This varies depending on the kind of data. For weather data an hourly sample rate may be sufficnt, but for high-quality audio the sampling rate is usually 4000-5000 Hz (samples per second). These are examples of a uniform sampling rate, but some data series have sporadic samples, so there is no fixed sample rate.
Used on Chap. 19: page 470