Dirsync - AAD Sync and AAD connect trying to understand

Hello all,

I'm learning about all the different tools and I wanted to ensure that my understanding of the 3 tools - dirsync, aad sync and aad connect are correct.

Dirsync 

Syncs on premise active directory the cloud - cannot sync from the cloud to on premise unless Rich Co-Existence is enabled and this only does it for a sub-set of users.

Azure Active Directory Sync 

.. I don't understand this one ? ... from reading though it looks as though AD Connect will replace AAD sync.

Azure Active Directory Connect 

Syncs on-premise to the cloud & from the cloud to on-premise