Oracle Database 18c (18.3) has officially been released for download on Linux  x86-64. See KM Doc 742060.1 for more details on the release schedule for other  platforms.

              

This is the first version of the database to follow the new yearly release  model.  Read KM Doc 2285040.1 for more details.  For practical  purposes, you can think of Oracle Database 18c as a Patchset of the Oracle  Database 12c release. However, instead of being named “Oracle Database 12c Release  2 12.2.0.2”,  the new naming structure reflects the year in which the  product released.
                   
Oracle Database 18c contains a lot of small, but extremely useful incremental  improvements, most of which focus on the three key marquee features in Oracle  Database 12c Release 2:

            

  •     Multitenant
  •     Database In-Memory
  •     Oracle Database Sharding

 

You can read more  details on the changes and improvements in Maria Colgan's Oracle Database blog post or in the Oracle  Database 18c documentation.