Definition - What does Index Defragmentation mean?
Index defragmentation is a part of Microsoft SQL Server maintenance where the index of database engine indexes of insert, update and delete operations is optimized to reduce fragmentation. This is done by reorganizing or rebuilding an index on an entire index or a single partition. Defragmentation improves disk space and performance of SQL Server.
Techopedia explains Index Defragmentation
Microsoft SQL Server maintains indexes of all the insert, update and delete operations performed on databases. Over time, these indexes can become fragmented or stored out of order on the database server's disks. This wastes disk space and can slow down database access operations. Fortunately, SQL Server offers tools to detect and repair fragmentation.
Index defragmentation is done through the SQL Server Management Studio and Transact-SQL. The indexes are defragmented by reorganizing or rebuilding an index. Indexes can also be rebuilt for individual tables for a database. Defragmentation makes sure that all the entries in an index are contiguous for faster and more efficient access instead of being spread out across multiple disks and partitions. It is similar to defragmenting files on a hard drive.