It means that once it has finished flowering, you can take the plant out of its present pot and put it in a larger one using Ericaceous compost.

And its only relevant if you're growing it in a pot... the meaning behind it is, its not good to plant out or repot a plant which is currently in flower because of the chances of root disturbance causing the flowers to drop, and to wait until its stopped flowering.

many thanks Owdboggy & Bamboo for your replies very helpful, although I a mature person not much of a gardiner