Priming is a special paint that seals the wood and promote adhesion to the final finish. Many doors now come primed from the factory and are ready for final finishing.
What does a primed door mean?
Primed Doors
The name refers to the fact that these doors have been pre-primed, often in white allowing you to paint them your desired colour without having to sand and prime yourself.
Can you leave a primed door unpainted?
Your primed door may arrive looking pretty finished, but it will still need to be painted. The primer will provide a smooth surface, covering the permeable surface of the wood. However, the paint is required to provide extra necessary coverage against wear & tear, temperature changes, water splashed and more.