Regarding the setting on Salesforce integration app

Hi,

I'm setting up some imports on Salesforce Integration app.
And I found a setting which is "Eloqua field update rule" for each field.

I can understand some of its options but I couldn't understand "Import Setting" and "Use Field Rule".
What do these mean? I couldn't find a document to describe this.
Before moving on, I'd like to know its meaning.

Best,
Hiroki