Relationships and Affiliations
What is a Relationship?
A Relationship in the Nonprofit Starter Pack is a relationship between two individuals (Contact records). So, for instance, relationships could be between friends, co-workers, manager/employee, parent/child, siblings, spouses/partners, etc.
NPSP Documentation: Create, Edit, and View Relationships
What is an Affiliation?
Affiliations are meant to express a relationship between a Contact and an Organization. For example, this could be an employment, volunteering, board-member, or other participation relationship. Affiliations can have attributes such as Role, Start Date, End Date, and Description, which are used to describe the relationship. Affiliations also has a status field to show if the relationship is “current” or “former”.
An Organization can have multiple Affiliations to express the relationship it has to many Contacts. And a Contact can have many Affiliations to show the relationship he/she has with many Organizations.
NPSP Documentation: Create an Affiliation with an Organization
What is a Primary Affiliation?
Only one of each Contact’s Affiliations can be “Primary”. This Primary Affiliation can be used to show which Organization a Contact is most affiliated with. That Organization's Name will appear on the Contact record, which makes reporting easier. It also means the Organization Name can be used in mail merges.
When you enter a "Primary Affiliation" record, NPSP will automatically create an Affiliation between that Contact and Organization (see Affiliations above).
You can define what "primary" means for your organization.
Note that Salesforce also offers features called Account Contact Roles and Account Contacts, but these aren’t used in the Nonprofit Starter Pack.
NPSP Documentation: Primary Contact vs. Primary Affiliation