The ECB's definition of euro area monetary aggregates is based on the following: A harmonised definition of the money-issuing sector. It consists of those entities which issue liabilities with a high degree of moneyness to non-MFIs located in the euro area (excluding central government). This sector comprises MFIs resident in the euro area. A harmonised definition of the money-holding sector, which comprises all non-MFIs resident in the euro area (except central government). In addition to households, non-financial corporations and financial institutions which are not MFIs are included, as well as state and local governments and social security funds. Central governments are considered to constitute a "money-neutral" sector, with one exception: central government liabilities with a monetary character (Post Office accounts, national savings accounts and Treasury accounts) are included as a special item in the definition of monetary aggregates. The harmonised definitions of MFI liabilities categories. These make it possible to distinguish between MFI liabilities according to their degree of moneyness, while also taking into account the features of different financial systems.

Source: https://www.ecb.europa.eu/stats/money_credit_banking/monetary_aggregates/html/hist_content.en.html