The default lookup is the by Lookup.getDefault(). It is the registry for global singletons and instances of objects which have been registered in the system by modules. The default lookup merges the contents of two places:* The meta-inf/services lookup -
this contains all objects registered by modules via the Java Extension Mechanism - putting files in the META-INF/services directory of their module JARs* The contents of the Services/ folder of the System (configuration) Filesystem
Note that the word "contains" is used loosely - nothing in the default lookup is instantiated until the first time it is asked for. For more details on lookup, see the general Lookup FAQ
The javadoc for Lookup can be found here.
Source: NetBeans FAQ