A swap line is a short-term loan made between central banks in order to provide liquidity and support the value of a currency when it is under threat. For instance, if the European Central Bank (ECB) requires dollars, it has the option of borrowing dollars from the Federal Reserve using a swap line as opposed to having to liquidate US treasury bonds. This works to mitigate fluctuations in currency values on foreign currencies, thereby making sure that negative foreign events do not have repercussions in the US. During the coronavirus outbreak, such swap lines in particular were used for the purpose of bringing ease into dollar funding markets and restoring them out of target levels.