Definition - Pull flows:
Pull flows are related to the processing of sales / procurement orders. A classical example of Pull flow is when a shop sells products to a customer. If the product is not in stock the product is sourced from a central warehouse or regional buffer.
When a product is sold in the shop a new procurement order is created Shop, it is converted into another procurement (B, via a Pull flow of type 'move') requested from the Holding. When procurement order B is processed by the Holding company, and if the product is out of stock, it can be converted into a Purchase Order (C) from the Supplier (Pull flow of type Purchase). The result is that the procurement order, the need, is pushed all the way between the Customer and Supplier.
Technically, Pull flows allow to process procurement orders differently, not only depending on the product being considered, but also depending on which location holds the 'need' for that product (i.e. the destination location of that procurement order).