I have a time series data of accelerometer in X,Y,Z axis. Data is not sampled at a constant sampling rate(but is close to 100 Hz). In the paper I am referring, it mentions that for feature selection I have to use 'windowing technique', with window of interval 4 seconds.
And the 'Features' that are extracted can be either time or frequency based features for the 'window'. So below features are extracted per window.
Time Based features : Mean, Maximum, Minimum, SD, Median
Frequency Based features : Mean, Maximum, Minimum, SD, Kurtosis
I understand the time based features but what does frequency based features mean ? Viz, How frequency based mean is different from time based mean.