Outsourcing - Outsourcing is subcontracting a process, such as product design or manufacturing, to a third-party company. Outsourcing involves the transfer of the management and/or day-to-day execution of an entire business function to an external service provider.
Offshoring - Offshoring describes the relocation by a company of a business process from one country to another – typically an operational process, such as manufacturing, or a supporting processes. Companies subcontracting in the same country would be outsourcing, but not offshoring.
Nearshoring - Nearshoring means sourcing service activities to a foreign, lower-wage country that is relatively close in distance or time zone (or both). Nearshoring is understood to mean that the business has reduced the complexity and risk of offshoring.
Offshore Outsourcing – Offshore outsourcing is the practice of hiring an external organization to perform some business functions in a country other than the one where the products or services are actually developed or manufactured.
All the definitions are modified from original source of Wikipedia.
Reference : Pinal Dave (http://blog.SQLAuthority.com)