The notions of offshore outsourcing, offshoring, nearshore outsourcing and nearshoring are very often used interchangeably.

Outsourcing:                http://en.wikipedia.org/wiki/Outsourcing
Offshoring:                  http://en.wikipedia.org/wiki/Offshoring
Nearshoring:                http://en.wikipedia.org/wiki/Nearshoring
Offshore Outsourcing:   http://en.wikipedia.org/wiki/Offshore_outsourcing 

More background intoramation:

http://www.bridge-int.nl/blog  - visit our weblog!
http://www.neoit.com/  
http://www.technology-evaluation.com/  
http://www.informationweek.com/outsourcing/