Units are different for electricity and gas; you can find more detail on what they mean in Your Bill Explained.

For electricity:

Units are different for each item:

• Rate type (e.g., Domestic Urban): Kilowatt hours (kWh)
• Standing charges: Number of days in your billing period
• PSO levy: Number of months in your billing period

For gas:

Units are different for each item:

• Rate type (e.g., Biggest Save eBundle): Kilowatt hours (kWh) – the unit for gas
• Standing charges: Number of days in your billing period
• Carbon Tax: Kilowatt hours (kWh) – the unit for gas