In time series analysis and forecasting, the baseline value, often denoted as ℓ(0), represents the initial level or baseline of the time series. It is an important parameter in some forecasting methods, like exponential smoothing. The baseline value is essentially the starting point for the forecast. It is used to initialize the forecasting process. For example, if you are trying to predict the sales of a product over time, the baseline value might represent the initial sales level at the beginning of your data.