Systemically Important Bank
From ACT Wiki
(SIB).
A bank whose disorderly failure would, because of its:
(i) Size,
(ii) Complexity, and
(iii) Systemic interconnectedness
cause significant disruption to the wider financial system and to economic activity in its (main) country or region of operation.
For this reason, SIBs are subject to more stringent regulation and capital adequacy requirements than other institutions.