Cuál es la diferencia entrebuild, runtime ycompile, enBuildConfig.groovy (1.3.7)

grails.project.dependency.resolution = {

    plugins {
        build "acme:acme-cache:latest.integration"
    }

    dependencies {
        build "com.foo.bar:foobar:1.0.5"       
        runtime "org.apache.httpcomponents:httpclient:4.0.3"
        compile("com.thoughtworks.xstream:xstream:1.3.1")
    }
}