The full moon of December is often called the Oak Moon.
December is the end of the year, when thoughts turn forwards and also back. We automatically consider the New Year as a time for a fresh start.
The oak is symbolic of this. The Celtic words for oak, duir or derw, have the same root as 'door'. And the oak was considered a gateway between lives, worlds, and spiritual stages of life. This is why the tree was sacred to the Druids - 'Druid' itself deriving from the same root.
The Oak King ruled over the dying year, superseded by the Holly King of the new year. The oak is the last of the deciduous trees to lose its leaves in winter - they hang on well into December - giving another connection to the dying year. The holly is of course evergreen, and symbolises the continuing thread of life throughout the months of death.
And so life goes on, through the doorway into the new year.