Question: what is a lag in time series?
Answer: A “lag” is a fixed amount of passing time; One set of observations in a time series is plotted (lagged) against a second, later set of data. The kth lag is the time period that happened “k” time points before time i. ... Lag1(Y2) = Y1 and Lag4(Y9) = Y5. The most commonly used lag is 1, called a first-order lag plot.