What is the WMR 4pm fix?

I hear portfolio momagers talk about the WMR 4pm fix price of currencies but what does it really mean?

WM - World Markets Company

R- Reuters

The WMR 4pm fix is a paid service to give subscribers the daily closing price of currencies which they can then use to conduct end of day and overnight transactions. The WMR price is usually fixed by 4pm London time every day.

Portfolio Managers find this service useful because they can all use the same spot price to settle their transactions and prepare for the next day.

The service was initialed by the Reuters company (in conjunction with World Markets company) but today other companies such as the London Stock Exchange also provide the same service for a fee.