The configuration for Apache Maven usage itself and projects built with resides in a number of places:
MAVEN_OPTS environment variable:This variable contains parameters used to start up the JVM running Maven and can be used to supply additional options to globally to Maven. E.g. JVM memory settings could be defined with the value -Xms256m -Xmx512m.
settings.xml file:Located in USER_HOME/.m2 the settings files is designed to contain any configuration for Maven usage across projects.
.mvn folder:Located with in the projects top level folder, the files maven.config and extensions.xml contain project specific configuration for running Maven.
The following guides contain further information to specific configuration aspects: