about source and target in maven-compiler-plugin

[Lin Ma]

Hello Maven masters,

For maven-compiler-plugin(a sample below), have a quick question. I read
this document (http://maven.apache.org/plugins/maven-compiler-plugin/), and
confused what means source and target 1.5 here, it seems it is an internal
version number of Maven, independent of JDK?

<plugin>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>2.3.2</version>
    <configuration>
        <source>1.5</source>
        <target>1.5</target>
    </configuration>
</plugin>

thanks in advance,
Lin