What is indexing and what are the different kinds of indexing ?

Answer 1

Indexing is a technique for determining how quickly specific data can be found.
Types:
1. Binary search style indexing
2. B-Tree indexing
3. Inverted list indexing
4. Memory resident table
5. Table indexing

Answer 2

Indexing is a way of sorting a number of records on multiple fields. Creating an index on a field in a table creates another data structure which holds the field value, and pointer to the record it relates to. This index structure is then sorted, allowing Binary Searches to be performed on it.

clustered, multi-dimensional clustered, unclustered, unique,
non-unique, b-tree, hash, GiST, GIN, full-text, bitmap,
partitioned, function-based.

For More Info.

http://www.msdn.microsoft.com/en-us/library/ms175049(v=sql.110).aspx

http://www-01.ibm.com/support/knowledgecenter/SSEPGG_9.5.0/com.ibm.db2.luw.admin.dbobj.doc/doc/c0020180.html?lang=en