I’m currently working on a shift policy and have some questions:
What is the definition of shift?

hmmm... tough questions.... well, the shift is the working pattern of the job, to describe the different working timing in the company.

Is working from 10am to 7pm considered a shift work as well? Our normal working hrs is 9am to 6pm.
Any timing can consider a shift work, if you have more than 1 working hour pattern in the company.

Is graveshift shift paid more than morning/afternoon shift?
This is usually the case, but it depends on your business needs, how difficult you need to recruit people to work on the shift and what types of employee profile you targeting.

For example, female employees in some of the trades prefer to work graveyard shift (eg. 11pm - 7am) and they do not like to work at afternoon shift (eg. 3pm to 11pm), because they wish to spend time with their children or family at evening time and night time.

How much is the average shfit allowance?
For graveyard shift, it varies from $8.00 to $25.00 per working day depening on which industry you wish to benchmark.