A Query, for purposes of this package, describes a set of selection criteria for a relational data model, regardless of whether it is, for example, from a SQL database.
When using POJava, you'll notice that the DaoTool supports several methods ending in "ByQuery". These methods are designed to support custom queries you create by extending AbstractQuery, which then support interfaces that translate those queries to one or more supporting persistence implementations, such as SQL, REST, WS*, Google Data API, or other API's such as one might use for an ESB.
This package includes one such interface, PreparedSqlProvider, that is understood by methods in the DaoTool. When properly implemented, your code will completely abstract its queries into classes serving a specific object type, such as WidgetQuery.class serving a Widget bean. The WidgetQuery can be used by a WidgetDao, which wraps any combination of methods from the DaoTool, plus any custom methods desired.