Source of truth
The system whose data is treated as correct when several systems show different values for the same thing.
Glossary · Systems & integrations
When the same data, such as a customer’s address, a stock level or an order status, is held in several systems, sooner or later the copies diverge. The source of truth is a decision, made in advance, about which system is believed when they do.
It is set separately for each kind of data: the source of truth for stock may be the warehouse system, for prices the online shop, and for customer contacts the CRM. Other systems receive that data but do not change it.
Without an agreed source of truth, an integration works until someone changes the same record in two places. Then one system overwrites the other, and nobody can tell which value was right.