This is the amount you earn & pay tax on. The figure required is your annual income before tax & stoppages. Additional income may be bonus, overtime, maintenance payments made through a court order. Ongoing state benefits can sometimes be used.
If you are self-employed then you use the “Total Income Received” figure from your SA302 tax computation. If you aren’t sure what this is then call your accountant & ask for the SA302 total income received figure for your passed three years of trading. If you haven’t been trading for three years, then enter the figure for the full years you have been trading.