Complex sentence: It is a form of outsourcing, in that the work is done by an outside contracted company rather than internally (insourcing), but unlike offshore outsourcing, the work is done in fairly close proximity to either the company headquarters or its target market.
Split into simpler sentences: It is a form of outsourcing, in that the work is done by an outside contracted company rather than internally (insourcing). But unlike offshore outsourcing, the work is done in fairly close proximity to either the company headquarters or its target market.