ETL is a extraction,transformation,loading tool i.e  u can extract , u can transform using different transformations available in tool  and aggreagte the data. The output of this ETL tool is used as input to OLAP tool

OLAP is online analytical process, where  u can get online reports after doing some joines,creating some cubes

ETL tools in market

1 INFORMATICA--  univeral tool ,good market

2 ABINITO --  fastest loading tool,very good market

3 DATASTAGE-- difficult work, no good market

4 BODI--  good market

5 ORACLE WAREHOUSE BUILDER--  good market