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 (eg. 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 (eg. Dom DF Gas Staff): 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