Understanding Maven tags - maven

Question

I was using maven in my project, most of the cases I used only dependency tags, but this time I have below tags in use:
<repositories>
<repository>
<id>myrepo</id>
<name>REPO</name>
<url>http://host:8081/nexus/content/repositories/repo/</url>
<layout>default</layout>
</repository>
<repository>
<id>thirdparty</id>
<name>THIRD</name>
<url>http://host:8081/nexus/content/repositories/thirdparty/</url>
<layout>default</layout>
<releases>
<enabled>true</enabled>
</releases>
</repository>
<repository>
<id>repo-snapshots</id>
<name>REPO-SNAPSHOTS</name>
<url>http://host:8081/nexus/content/repositories/snapshots/</url>
<layout>default</layout>
<snapshots>
<enabled>true</enabled>
</snapshots>
</repository>
<repository>
<id>repo1-snapshots</id>
<name>REPO1-SNAPSHOTS</name>
<url>http://host1:8081/nexus/content/repositories/snapshots/</url>
<snapshots>
<enabled>true</enabled>
<updatePolicy>always</updatePolicy>
</snapshots>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>myplugin</id>
<name>MY-PLUGIN</name>
<url>http://host:8081/nexus/content/repositories/central/</url>
<layout>default</layout>
<releases>
<enabled>true</enabled>
<updatePolicy>never</updatePolicy>
</releases>
</pluginRepository>
</pluginRepositories>
<distributionManagement>
<repository>
<id>distr</id>
<name>DISTR</name>
<url>http://host:8081/nexus/content/repositories/releases/</url>
</repository>
<snapshotRepository>
<id>distr</id>
<name>DISTR</name>
<url>http://host:8081/nexus/content/repositories/snapshots/</url>
</snapshotRepository>
</distributionManagement>
I know that repositories is used to configure our remote repositories.
1) But what is the use of releases --> enabled = true indicates
2) also what it indicates when we say snapshots --> enabled=true instead of using releases.
3) Also what it indicates if we say updatePolicy=always and what happens if we do not mention this.
4) What is the use of pluginRepositories here? also the inner releases tag
5) What is the use of distributionManagement and its inner tags repository and snapshotRepository?

Answer 1

1) This means that Maven searches release versions (aka non-SNAPSHOT versions) in this repository.
2) Maven searches SNAPSHOT versions in this repository.
The distinction between (1) and (2) exists because if you do not have repository groups, you usually have different repositories for the different types.
3) This means that SNAPSHOTS are always (read: every build) updated from remote repositories. The standard policy is to cache downloaded SNAPSHOTs for one day (so triggering another build on the same day would not again download the newest SNAPSHOT).
4) These repositories are purely used for the dependencies of your plugins.
5) These are used to deploy artifacts you build yourself.