I am a bit confused regarding the actual definition of structural unemployment. Some places say that it is the permanent decline of a particular industry, leading to workers being unemployed as they are occupationally immobile.
Other sources say that it is a change in the structure of an economy (e.g. from secondary to tertiary), usually brought about by changes in technology. (Also, just another question, how exactly does improved technology help convert an economy from being mainly secondary to being mainly tertiary?)
So, could you please provide a rock-solid definition of 'structural unemployment'?
Answers would be very much appreciated.