This is defined in the UK Ionising Radiations Regulations 2017 (IRR17) as the use of ionising radiation to sterilise, process or alter the structure of products or materials. Often the term 'Industrial Sterilisation' is used to mean the same thing where ionising radiation is used (although non radiation techniques such as ethylene oxide processing could also be defined by the same term). 

When considering the term for use with the UK IRR17,  it represents the primary intention (e.g. sterilisation, cross-linking, polymerisation and similar) - often termed a specified practice (i.e. 'industrial irradiation'). Although use of x-rays for producing an image of an object could in theory have sterilising  / structural changing potential, it would not be treated as industrial irradiation as this is not the primary intention. 

Some typical applications of industrial irradiation

Medical device sterilisation: Large industrial irradiators using radioactive Co-60 (or electron beam / x-ray systems) can deliver high doses in the 10-50 kGy region to sterilise medical consumables, equipment and implant devices (e.g. replacement joints).

Food sterilisation: Large doses of ionising radiation can kill bugs / insects and larvae, slow ripening process, and inhibit sprouting in fruits, vegetables, and grains. It can also be used to kill salmonella bacteria in meat products (particularly in poultry). Food sterilisation does not take place in the UK although ingredients used in UK sold produce may have been irradiated elsewhere in the world. Typically several kGy are used depending on product type. 

Changing the properties of materials (e.g. strengthening): Industrial irradiation can be used to modify the chemical, physical or biological properties of materials. This often uses electron beam systems  - for example flexible rubber pipework can be formed into shape and then 'fixed' (hardened). 

Gemstone colour change: Irradiation using intense electron beams (or gamma rays from Co-60, or neutrons from a nuclear reactor) can be used to alter the colour of gemstones, potentially increasing their value. For example, topaz can be turned from white to pale yellow or blue depending on the irradiation technique. 

Ion Implantation:  Accelerators are often used in ion implantation.  Semiconductor doping and surface finishing are example applications.