In the Local field mapping settings, you answer the question, what name does the external database use for the course? In the following screenshot, you can see that you have three choices:

In Moodle, every course has an ID. The front page of your Moodle site is always course number 1. The next course that you create is course number 2 and so on. In your external database, you can use this ID to specify your courses. However, I recommend against using the ID in an external database; let me explain why.

Suppose you install a new version of Moodle. Then, you export your courses out of your old Moodle installation. Now, suppose you import those courses into your new Moodle installation. The first course that you import will have an ID of 2. The second course that you import will have an ID of 3 and so on. These course IDs might be different from those in the external database. Therefore, when you connect your new Moodle site to the external database, the course IDs will no longer match.

Consider using the idnumber or shortname of the course in the external database. One advantage of using the shortname is that this is a required field for every course, so you know that every course will have one.

The shortname is used in the navigation bar at the top of the page. In the following screenshot, the shortname of the course is Scientific Method 1:

The idnumber of a course is optional. Students will not see the idnumber; only administrators and teachers see it.