The simple explanation is that when you load new data into your software, you use data import. For example, when migrating data from one app to another or testing a new app.
When you wish to add information to existing data or edit something in your database, you should use data update. For example, to establish relationships between subsidiaries and parent companies, or to assign a large number of tickets to certain users in your helpdesk.
Loader also allows you to import data while updating. Create an account
and see how it works for free.