LTRO = Long-Term Refinancing Operation

LTRO was used by the ECB as an alternative to QE. It enables European banks to borrow as much money as they want at a low rate. They have been using this as a carry trade (using it to invest in sovereigns with a much higher yield). It has the effect of driving down the yield on sovereign debt, meaning the sovereigns have to pay less in interest on their debt, aiding their situation.