The MSI measure the flow of monetary services received each period by households and firms from their holdings of monetary assets (levels of the indexes are sometimes referred to as Divisia monetary aggregates).
Source: Anderson, Richard G.
Source: Jones, Barry E.
Release: Monetary Services Index (MSI)
Anderson, Richard G. and Jones, Barry E., Monetary Services Index: M1 (preferred) [MSIM1P], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/MSIM1P, May 26, 2016.