"Lacking definition", as I call it, is explained on page 46 of the 2010 report (Note 3: Survey Universe).
These libraries are included in the data files because they qualify as public libraries under state law. However, beginning with the FY 2010 report, the 290 non-FSCS libraries are excluded from the tables, for a total of 8,951 public libraries in the 50 states and the District of Columbia. The Institute of Museum and Library Services defines the 3 administrative entities of public library administrative structure as follows.
What are non-FSCS libraries, you might ask?
Public libraries that don't measure up to this 5-point definition developed by the Federal-State Cooperative System.
Sidebar: The numbers 9225 and 8951 represent one of 3 administrative entities that are used in the IMLS reports.
The number of stationary outlets (central libraries and branches) also declined from 16,698 in 2009 to 16,417 in 2010.
The following state-by-state overview gives you indication of where public libraries lacking definition are located. (Sorry, my subtraction doesn't match the IMLS when I compare tables 1 and 3 in the 2009 and 2010 reports.)
This table makes it clear where libraries lacking definition are most prominent.