The data components of a file. In this case it addresses whether the file is healthy.
When Hard Disk corruption or viruses affect the structure of a file it means that the file has become damaged beyond repair.
A file is like a tower, with a perfect structure, the right text. If the file structure is damaged it acts as a tower which concrete wall has been damaged.
A file with a healthy, or acceptable data structure will do what is supposed to. An unhealthy file may cause your computer to crash, or freeze; or it might make certain programs behave erratically.