System of Record
A system of record is the authoritative source for a particular type of company data: the CRM for customers, the HR system for employees, the ledger for finance.
The same fact usually exists in several places. A renewal date appears in the CRM, in a spreadsheet, in a slide and in an email thread. Only one of those is authoritative, and knowing which is what keeps a company consistent with itself. That designation is the system of record.
For AI it matters twice. Reading, because an answer should come from the authoritative source rather than the most recently mentioned copy. Writing, because an agent that updates the copy instead of the record leaves the company more inconsistent than before it started.