Data Migration vs Data conversion

When we need to enter data into oracle Apps:

• The Data can be entered using the application Screens (for small amount of data, like creating PO, entering sales orders using Oracle Apps screens).
• The data can be entered using Oracle’s Open System Interface (for regular operations e.g. for moving data from one module to another).
• The data can be stored in the database table directly (Not recommended by oracle and can be very risky, because on any event data is going to be stored in many tables and data should be validated before inserting into tables that may cause data integrity and inconsistency problem, sometimes it may corrupt the data completely.).
• Using third party tools like data loader (It is also can be used when data is relatively small (25-200 records) because it captures the keystrokes and works like manually entering the data into Oracle form but much faster as process is automated).

Read Need of Migration/Conversion

Migration: Migration of data means moving the data from one system to another using Interface Programs/APIs where both the systems have same structure of data.
Process of Migrating of data:

• Identify the data to be imported to new system (Business requirement).
• Extract the data into flat file/Staging table
• Load the data into Interface Table(using SQL* Loader/DB Link/Others) after validation(If loading the data using Interface)

Conversion: Conversion of data means translating the data to suite target system (data should be formatted according to target system )  and then move the translated data using Interface Programs/APIs.

• Identify the data to be imported to new system (Business requirement).
• Extract into flat file/Staging table
• Translate/Convert/Format the data
• Load the data into Interface Table(using SQL* Loader/DB Link/Others) after validation(If loading the data using Interface) and then launch standard Interface concurrent program to load the data to Oracle Apps Base Tables
• If using API, fetch the data, validate it and then call API to import the data

Also Read Difference between Migration/Conversion and Interface