What are "lagged values" from autocorrelation topic

What are “lagged values” from autocorrelation topic? What is the difference from “normal values”?

You are working with a time series of data. What this essentially means is you take the original time series and create a second time series of data by -1 periods. The (t-1) data is the lagged data (see the pattern below).

Period / (t) / (t-1)

1 / 8.5 / –

2 / 3.1 / 8.5

3 / 2.5 / 3.1

4 / 4.8 / 2.5

etc.