There are seven levels of Hadeeth

1. A Hadeeth that was collected by both al Bukhari and Muslim.
2. A Hadeeth that was collected by al Bukhari but not by Muslim.
3. A Hadeeth that was collected by Muslim but not by al Bukhari.
4. A Hadeeth that is authentic according to the conditions of both al Bukhari and Muslim but was not collected by either of them.
5. A Hadeeth that is authentic according to the conditions of al Bukhari but was not collected by him.
6. A Hadeeth that is authentic according to the conditions of Muslim but was not collected by him.
7. A Hadeeth that is authentic according to the conditions of other scholars of Hadeeth who collected only authentic Ahadeeth [such as Ibn Khuzaymah and Ibn Hibbaan in their Saheehs].