In reply to manoj.

Complicated, in which the relationship between cause and effect requires analysis or some other form of investigation and/or the application of expert knowledge, the approach is to Sense - Analyze - Respond and we can apply good practice. [e.g. an airplane is complicated, as all its parts can be known]

Complex, in which the relationship between cause and effect can only be perceived in retrospect, but not in advance, the approach is to Probe - Sense - Respond and we can sense emergent practice. [e.g. weather is complex, as the entire system is not knowable, though patterns can be sensed]

Source: http://en.wikipedia.org/wiki/Cynefin

Complex work is dealing with complex situations, phenomena, or problems. These are sometimes referred to as tough problems http://jarche.com/2005/06/old527/ or wicked problems http://jarche.com/2012/06/a-wicked-problem/