1, The full form of SDR is Software Defined Radio. It’s used on Academic & Science ,Electronics in Worldwide

Software Defined Radio attempts to place much or most of the complex signal handling involved in communications receivers and transmitters into the digital (DSP) style.  In its purest form, and SDR receiver might consist simply of an analog-to-digital convert chip connected to an antenna.  All the filtering and signal detection can take place in the digital domain, perhaps in an ordinary personal computer.  While there are still good reasons to use some analog components in high-performance gear, the SDR approach is becoming more common in Amateur Radio.

2, The full form of SDR is Special Drawing Rights. It’s used on Business ,Trade in Worldwide

The SDR is an international reserve asset, created by the IMF in 1969 to supplement its member countries’ official reserves. So far SDR 204.2 billion (equivalent to about US$281 billion) have been allocated to members, including SDR 182.6 billion allocated in 2009 in the wake of the global financial crisis. The value of the SDR is based on a basket of five currencies—the U.S. dollar, the euro, the Chinese renminbi, the Japanese yen, and the British pound sterling.

The SDR was created as a supplementary international reserve asset in the context of the Bretton Woods fixed exchange rate system. The collapse of Bretton Woods system in 1973 and the shift of major currencies to floating exchange rate regimes lessened the reliance on the SDR as a global reserve asset. Nonetheless, SDR allocations can play a role in providing liquidity and supplementing member countries’ official reserves, as was the case amid the global financial crisis.

The SDR serves as the unit of account of the IMF and some other international organizations.

The SDR is neither a currency nor a claim on the IMF. Rather, it is a potential claim on the freely usable currencies of IMF members. SDRs can be exchanged for these currencies.

3, The full form of SDR is Santander Airport. It’s used on Transport & Travel ,Airport Codes in Spain

Santander Airport (IATA: SDR, ICAO: LEXJ), officially Seve Ballesteros–Santander Airport is an international airport near Santander, Spain and the only airport in Cantabria. In 2018 the airport handled 1,103,353 passengers and 11,258 flights, far more than in 1995 when it handled only 180,00 passengers. Since then, the traffic has declined following the trend in Spanish airports and the decrease in operations by some of the companies

Santander Airport is located south of the city, the port of Santander is situated between the airport and the city. At a short distance from the airport is the S-10, it connects the A-67 and A-8 motorways with each other. Because of this, cities east (Bilbao) and west (Gijón) of Santander Airport are easily accessible as well.