There is no definition of portable appliance, but there is guidance. Best practice would suggest that an inventory of equipment is made to ensure that there is a record of what needs testing.
The frequency of inspection is not legislated for and will depend on the item being tested. Some items may not need not to be tested for five years, whereas others might be best tested every 12 months.
For further and more detailed information on this please see our briefing paper on Electrical tests and gas safety checks for church buildings.