If a user is granted write permission to a file, it means the file can be modified and overwritten.
If a user is granted write permission to a directory, it means the contents of the directory can be changed. This means that files can be added and removed. It also means that the permissions of files can be changed. Note that it is possible to set up a directory as writeable, but the files contained as read-only. We will discuss interesting scenarios like this later.