DB: Clustered Indexes or Index-Organized Tables

Reading
http://www.javacodegeeks.com/2012/02/20-database-design-best-practices.html

I stumbled on this statement:

"Use indexes for frequently used queries on big tables. Analyser tools can be used to determine where indexes will be defined. For queries retrieving a range of rows, clustered indexes are usually better. For point queries, non-clustered indexes are usually better."

What is a "clustered index"?

http://en.wikipedia.org/wiki/Database_index#Clustered
"They are known as "index organized tables" under Oracle database."

Pretty good description here:

http://www.orafaq.com/wiki/Index-organized_table

More here:

http://stackoverflow.com/questions/3382939/when-should-i-use-oracles-index-organized-table-or-when-shouldnt-i

"In practice, index organized tables are most likely to be reference data, code look-up affairs."