What are tags and filtering in JUnit 6 and how are they used?

// Annotate tests with @Tag
@Tag("fast")
@Tag("unit")
class FastUnitTest {
    @Test void test1() { ... }
}

@Tag("slow")
@Tag("integration")
class SlowIntegrationTest {
    @Test void dbTest() { ... }
}

// Composed annotation to avoid repetition:
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Tag("fast")
@Tag("unit")
public @interface UnitTest { }

@UnitTest  // same as @Tag("fast") @Tag("unit")
class OrderServiceTest { ... }

<!-- Maven Surefire: run only fast unit tests -->
<plugin>
    <artifactId>maven-surefire-plugin</artifactId>
    <version>3.3.0</version>
    <configuration>
        <groups>fast & unit</groups>
        <excludedGroups>slow | integration</excludedGroups>
    </configuration>
</plugin>

<!-- ConsoleLauncher: tag expression syntax -->
java -jar junit-platform-console-standalone-6.1.1.jar \
    --scan-class-path \
    --include-tag "fast" \
    --exclude-tag "slow"

# Gradle: filter by tag
test {
    useJUnitPlatform {
        includeTags "fast"
        excludeTags "slow", "integration"
    }
}