Apex Dataloader

Definition: Apex Data Loader is a local system software that can import data into salesforce.com.
It is a client Application for bulk import/export of data.

Apex Data Loader van move data into/out of any SF.COM RECORD,including opp.,&contact.

When Importing data -It reads,extracts&loads data from CSV files
When Exporting data-it outputs CSV files.

Various Operations that can be performed through Apex Data Loader are:
A)Insert
B)update
C)Upsert
D)delete
E)Export

Importing Data through Apex dataloader to SF.COM?
UR NAME---SETUP---ADMIN SETUP---DATA MANAGEMENT---DATALOADER
--DOWNLOAD DATALOADER

Maximum limit to import data is 50k records/session.
If we have more than 50k records to import ,then go for DATA LOADER.