The SDR is an international reserve asset, created by the IMF in 1969 to supplement its member countries' official reserves. Its value is based on a basket of four key international currencies, and SDRs can be exchanged for freely usable currencies. With a general SDR allocation that took effect on August 28 and a special allocation on September 9, 2009, the amount of SDRs increased from SDR 21.4 billion to SDR 204.1 billion (equivalent to about $ 321 billion). http://www.imf.org/external/np/exr/facts/sdr.htm

It confuses me too!