Taken from Carol Nash guide.
Multiple places of work is business, same goes for car insurance.
Social & domestic: When you use your motorbike for social use only, such as riding with friends or going to the shops, and not for any commuting or work-related purposes.
Commuting: As well as using your bike for social and domestic reasons, you may also use it to regularly travel to one permanent place of work.
Business use: This is for when you travel to more than one place of work, such as a training course, bank, or other work-related destination. You must tell your insurer even if it’s just a one-off journey, otherwise you’re at risk of invalidating your policy. Should your work situation change and you need to use your bike to travel more, let your insurer know straight away.