Resampling is simply mimicking the process of sampling
by choosing another sample at random from the population based on data from your sample.we sample instead from an artificial population constructed on our computer and that embodies everything we know
about the population of interest. In many, but not all, of the examples
that follow, this artificial population is the very data set from which
we seek to draw inferences. Since the data set is itself a sample of the
whole population, we are taking a sample from the sample: resampling.
This doesn’t, of course, provide more information about the population,
but it does provide us with a way of understanding the consequences of
sampling variability for drawing inferences about the population based
on our data.