External fund numbers are typically utilized by organizations that have multiple support areas nested under their primary profile. Essentially, this feature eases the reconciliation process by applying the provided external fund number to each applicable gift on your reporting page.
Example 1: A university may have an Athletics department that is fundraising for all of their varsity sports. Under the primary Athletics profile, the university has created a support area for Softball, Volleyball, and Field Hockey.
Example 2: A Veterans Resource Center is raising funds for multiple campaigns. Any gift to their primary profile, Veterans Resource Center, will be used to support their general programming. Support areas have been created for Camp Restoration and Career Training, allowing donors to make a gift to those specific efforts.
In both of the examples above, utilizing external fund numbers would make it easier for the reconciliation team to quickly identify where specific funds should be routed once they are paid out. If your organization does not need to use this feature for reconciliation purposes, you are safe to ignore it!