Hi Ejas,
Inbound proxy is used when ECC receives data from any third party system while outbound proxy is be used to push data from ECC to any third party system.
If you want to know the development difference, go through this link. It covers both Inbound and Outbound proxy development.
ABAP Proxy (Complete Developments on SAP-PI & SAP-ABAP Systems)
Regards,
Abhishek
