In one sentence
A source of truth is the place a workflow treats as correct when it needs a particular piece of information.
The simple model
For any fact the work depends on, the current price, the customer's address, the order status, some place has to be the one that is right. That place is the source of truth for that fact.
The trouble starts when there is more than one. If the price lives in an ERP, a spreadsheet and an old PDF, and they disagree, nobody knows which is correct without asking a person.
Why you care
A workflow can only be as reliable as the information it trusts. If the source of truth is unclear, both people and AI will sometimes use the wrong version, confidently.
This matters even more with AI. A person often senses when a number looks stale and double-checks. An AI will use whatever it is given and produce a convincing answer from outdated information.
In practice, there are often several
Discovery frequently reveals three "sources of truth" for the same fact, because different departments each maintain their own copy. This is normal and not a moral failing. But before automating, you usually have to pick one and make the others follow it, or the workflow inherits the confusion.
Source of truth vs a copy
A copy can be useful for speed or convenience, as long as everyone knows it is a copy. The danger is when a copy quietly starts being edited and becomes a second source of truth. Then two places are both "correct" and they drift apart.
A small example
A support team quotes delivery dates. Some staff check the logistics system, others use a shipping schedule pasted into a chat weeks ago. Customers get different answers. Naming the logistics system as the single source of truth, and retiring the pasted schedule, fixes the inconsistency without any AI at all.
What this does not solve
Naming a source of truth does not make it correct or current. The named source still needs an owner who keeps it accurate. A single wrong source is easier to fix than several disagreeing ones, but it still needs maintenance.
