The name itself states this. Autocorrelation and autoregression. It regress on it's past values hence the "auto". We're interested on past value so each other value is dependent on the past.
An example of this is taking blood pressure. You would assume that taking blood pressure two consecutive days means that the previous day is highly correlated to the present day test.
Where as if you compare your blood test a year ago compare to today blood test it won't be as correlated. This is why ARIMA is dealing with correlation with time lags/lengths.
The name itself states this. Autocorrelation and autoregression. It regress on it's past values hence the "auto". We're interested on past value so each other value is dependent on the past.
An example of this is taking blood pressure. You would assume that taking blood pressure two consecutive days means that the previous day is highly correlated to the present day test.
Where as if you compare your blood test a year ago compare to today blood test it won't be as correlated. This is why ARIMA is dealing with correlation with time lags/lengths.