What are the special stocks used in MM? | SAP-MM

Special stocks are the stocks that are managed separately irrespective of the fact whether or not they belong to your company. The company manages a material by using a data record, which contains all the required information.
The different types of special stocks are as follows:
=>    Sales order stock
=>    Returnable packaging with customer
=>     Consignment stock at customer
=>        Vendor consignment stock
=>      Returnable transport packaging
=>     Subcontracting
=>     Pipeline.