There are 3 types of data dependency. They are:

1. RAW (read after write) dependency.

2. WAW (write after write) dependency.

3. WAR (write after read) dependency.

The first one is a true dependency. The last 2 are false dependencies and can be removed through register renaming.

You can google for detailed explanation and you will get the answer. These concepts are discussed in any good Computer Architecture book. 

One such book is - "Parallel Computer Organization and Design".

https://www.amazon.com/Parallel-Computer-Organization-Design-Professor/dp/0521886759/ref=mt_hardcover?_encoding=UTF8&me=

I hope I answered ur queries. Good luck.

Regards,

Sritam Paltasingh.