Business email compromise is the broad category: any attack that uses a trusted business email identity to move money or data. CEO fraud is one variety of it, where the impersonated identity is a senior executive. CEO fraud is a subset of BEC, not an alternative to it.
The distinction matters for defence. If you only train staff to distrust emails from the chief executive, you miss vendor impersonation, payroll diversion and legal-counsel pretexts, which are all BEC and none of them CEO fraud.
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