What does ghost writing mean?

ghost writing means that you write and creat and editing content of a book, article, poems ... etc, under a name of someone else 

Ghost writing is usually when a writer is writing in the style and voice of someone else and the finished product is then written in the name of the client. E.g. if someone wants to write an autobiography in his own voice, but has no writing ability, they sometimes hire ghost writers to write for them in their style and voice, however the client then sells it as his own product. 

The ghost writer gets no credit, thus the use of the word ghost.

It means you write something but it gets signed by someone else's name. An example of this is marketing emails or speeches.