Featurization using identifier column

Can you kindly provide more information on the below mentioned under the featurization step:
https://docs.microsoft.com/en-us/azure/machine-learning/how-to-auto-train-forecast#configure-experiment

"Create features based on time series identifiers to enable fixed effects across different series"

What kind of features are these? Can you provide a simple example?
Do you have any literature references?

Thank you for your help