The business logic layer is the part of an application or workflow where the real rules are applied: calculations, validations, branching decisions, and data transformations. It sits between raw inputs and final outputs, turning source data into something the organization can use. In a finance or reporting process, this layer may handle reconciliation rules, tax formulas, approval thresholds, and exception handling.
In cyber security, this layer matters because attacks often target the rules, not just the code. Business-logic flaws can let an attacker bypass checks, change amounts, trigger unauthorized actions, or exploit edge cases that developers did not expect. Defenders want this layer to be visible, testable, and auditable, because hidden logic is hard to review and easy to misconfigure. Strong controls such as code review, workflow logs, versioning, and separation of duties help teams prove what the system did and detect tampering or abuse.