Money Supply means the ECB's monetary aggregates, stocks of short-term liabilities counted as money, for the euro area. It covers only the euro area and only holdings by residents outside MFIs and central government. It never covers the whole EU, and its composition changes as euro membership changes. It is a census-like full count, not a sample.
The series started in December 1998 and appears monthly. Headline M3 (broad money) reports annual growth; M1 (narrow money) holds cash plus overnight deposits, while M2 (intermediate money) adds short-term deposits. M3 adds market instruments: repos, fund shares and MFI debt securities up to 2 years; loans are counterparts, not money itself. Small MFIs keep derogations within 5% of national balance sheets, grossed up to full coverage in millions of euro.