High Impact

The loss of confidentiality, integrity, or availability that could be expected to have a severe or catastrophic adverse effect on organizational operations, organizational assets, individuals, other organizations, or the national security interests of the United States; For example:

1. causes a severe degradation in mission capability to an extent and duration that the organization is able to perform its primary functions, but the effectiveness of the functions is significantly reduced;
2. results in major damage to organizational assets;
3. results in major financial loss; or
4. results in severe or catastrophic harm to individuals involving loss of life or serious life-threatening injuries.

See the following for more information: 

CNSSI 4009-2015 (FIPS 199).
NIST SP 800-161 under High Impact (FIPS 199, CNSSI 4009).
NISTIR 7622 under High Impact (CNSSI 4009-2010, FIPS 199).