The processes in supply chain fall into two types of categories i.e. Pull processes and Push processes.
Pull Process depends on the customer demand whereas Push processes are the predictions, i.e. manufacturer produces gooods and services thinking that there will be demand or requirement for the product or service produced.
Pull processses depend on the reactions of the customer. On the other hand push processes are not actual demand.
For ex. Mobile Mfg. companies assembles parts to produce mobile phone. The process before production of the phone is Push Process but the process after production is Pull Process, as the manufacturer is predicting that the product will be accepted. As the customer orders for mobile phone it will become Pull Process.(Actual demand).
In supply Chain the orders can be taken through websites or by telephonic marketing. Those are known as "Mail order Supply Chain".