This category will have a balance in it, if all of the VAT on your purchases is greater than the VAT on your sales for your current VAT period. When you lodge your return and HMRC pays you for the amount outstanding, this will net off to zero for the period lodged.
What's included
When the VAT on all of your purchases outweighs the VAT on your sales - HMRC then owe you this balance when you have lodged your return.
What's not included
Any of the other taxes such as corporation tax, PAYE or NI contributions.
Additional Information
It's worth noting that HMRC may not always pay this balance to you. Instead, they might hold the balance in your VAT account to, either partially or fully, offset a future payment. If you want the refund you should phone HMRC in order to arrange it.
You should only categorise to this category if you are receiving a VAT refund