Espionage also called spying involves an individual or a firm obtaining information considered secret or confidential without the information of the person holding on to such information. It is considered an illegal activity throughout the world. Industrial espionage, personal espionage and corporate espionage are forms of espionage which are done purely for commercial purposes and would not involve threats to national security.
With respect to industrial espionage it basically means removal copying, removal or recording of confidential information of a company by a competitor to gain unlawful access of his trade secrets. The difference between competitive intelligence and industrial espionage is that while competitive intelligence is legal, industrial espionage is illegal.
Industrial Espionage is basically associated with heavy-industries like Automobile and Computer, as these industries involve a lot of investment in Research and development. It will involve practices like technological surveillance, bribery, black mail and trade secrets.