In plain language
When two apps disagree about a customer’s email, the source of truth decides which one is right.
Example
The CRM is the source of truth for contacts, so the email tool only receives updates from it.
Related terms
Sync (One-Way and Two-Way) · CRM · Deduplication · Data Mapping
Common misconception
Syncing two apps both ways does not create two sources of truth; without clear ownership, edits conflict and overwrite each other.
Implementation guidance
Choose one owner per data type, document which fields each system may edit, sync outward from the owner, and lock or hide fields elsewhere.