The airlines (at least those operating in the IATA environment) refer to "Taxes, Fees and Charges (T/F/C)". There have always been government imposed taxes - for instance the American "Transportation Tax" which, over the years has varied between 8 and 10% of the fare. Some countries (Germany and Italy spring to mind) charge VAT on air fares.
When the EU was about to stop duty free sales the airlines became worried that the airports would lose shopping revenue and that they would recoup that by charging the airlines more. As others have noted, airlines have always paid airports for the use of facilities. The airlines would have had little choice (they said) but to pass on the increase in the form of higher fares. The airlines therefore chose to show that airport fee as a separate T/F/C. In reality shopping levels didn't really change so the fees remained (roughly) the same. Airlines negotiate their own fees with each airport.
However, the flood gate had been opened and we now find ourself in the situation where all sorts of things end up as a T/F/C.
If you want to know all the codes and what they mean see
http://www.geo.at/reiseinfos/doks/list_of_tax_codes.pdf In the case of the OP you need to look at the codes applied by the UK, US and then look at the "Miscellaneous Codes" at the very end of the list. Worth noting the YQ and YR are often used for fuel and insurance charges. OA might be used if an airline charges you to make the booking over the phone or even via certain distribution channels (read travel agency, GDS) and OB if they impose a fee for paying with a card.