1. Internal Fragmentation
2. External Fragmentation
Internal Fragmentation:- In this fragmentation, there exists a space between the different records within a page. This is caused due to the Insert, delete or Update process and due to this Index takes more space than it needs to and it result in more read operation during scanning. It can also be caused due to the low value of fill factor of the page which determine how much % of the page should be used for storing the records.
External Fragmentation:- In this fragmentation, the extents of the table is not physically stored continuously on the disk which causes the jump from one extent to another extent which takes longer time.
Both the fragmentation can be resolved by Rebuilding or Reorganization of the indexes of the tables.
For Rebuilding or Reorganization of the indexes , please refers the below link: