What is difference between PSA and ODS?

PSA: This is just an intermediate data container. This is NOT a data target. Main purpose/use is for data quality maintenance. This has the original data (unchanged) data from source system.

ODS: This is a data target. Reporting can be done through ODS. ODS data is overwriteable. For datasources for which delta is not enabled, ODS can be used to upload delta records to Infocube.  

You can do reporting in ODS. In PSA you can't do reporting directly

ODS contains detail -level data , PSA The requested data is saved, unchanged from the source system. Request data is stored in the transfer structure format in transparent, relational database tables in the Business Information Warehouse. The data format remains unchanged, meaning that no summarization or transformations take place

In ODS you have 3 tables Active, New data table, change log, In PSA you don't have.  *-- Naveeen Kumar