Taxable Remittance?

I see that the Sales Activity page of the developer site has finally been fixed to only show the current month (hurray!), but I noticed a new value at the bottom labelled "Taxable Remittance". What is this? A Google search returns a lot of UK based results, but nothing of particular help in deciphering what it means with respect to channel sales. Could we please get some details on this? Thanks!