Approved Scanning Vendor ASV
Someone who determines if an organization is compliant with PCI DSS external scanning requirements.
ASVs perform an external vulnerability scan of an organization’s network or website from the outside looking inward. In addition to determining if it is PCI DSS compliant, these scans from service providers can provide insight into any data security changes that need to be made.
All compliant companies need a quarterly network scan by an Approved Scanning Vendor (ASV). A list of these can be found here.