Getting off scot-free refers to someone getting away without payment, either monetary or otherwise. In fact in modern usage, it often refers to suspects who are not convicted of a crime. If a person feels that the suspect should have been convicted, he might say, “That guy is getting off scot-free.”
Often the term is confused with the frugality that is occasionally attributed to the Scottish. Actually, the term scot predates old Gaelic that would have been spoken by the Scots. In fact the word has its origins in Scandinavian language and probably descends to the English language via Anglo-Saxon.
Scot literally translates to payment. Thus getting off scot-free is not having to pay the payment, or is payment free. In medieval England, occasionally people paid a tax called a scot that would have been used to fund relief programs for the exceptionally poor, not that such relief programs were many.
The scot one paid was also called a lot, shorted for allotted share of the payment. The two terms naturally married, producing one word for both payment and share. If a person could avoid making a payment in some way, he was getting off scot-free.
Now a scot could stand for any type of payment, and is often used when discussing paying a tab at the bar. Each person drinking owes a scot, a portion of a shared tab. A person who doesn’t pay his scot is getting off scot-free.
Getting off scot-free implies evasion, purposeful or otherwise of the dues one is supposed to pay. It is frequently an annoyance to others if people duck out of paying what everyone else must pay. This is especially the case if the scot of a bar tab is avoided, since everyone else will have to pay extra to make up for the person getting off scot-free.
It is good to know that a term in frequent usage is not in fact a racial slur intended to insult the Scottish. Many terms in frequent usage do have their origins in language that deliberately insults race or gender of others. Fortunately, scot-free is free of this taint.