Significant institution
From ACT Wiki
Bank supervision.
(SI).
1. European Central Bank (ECB).
A bank considered significant enough to be supervised directly by the ECB, rather than by a national supervisory authority.
Criteria for determining a bank's signficance in this context include its size, economic importance, and whether it has received or requested direct public financial assistance.
2.
Similarly important banks and other institutions in other supervisory systems.