Tim Bowen sheds some light on the origins and definition of the phrase to get off scot free.
If you get off scot free you avoid punishment for doing something that deserves punishment. For example, “Although the police caught him red-handed, the judge said there wasn’t enough evidence and he got off scot free”.
The word scot in this sense has nothing to do with Scotland or Scotsmen, however. Scot is believed to be a word of old Germanic origin that is related to the words shot and shoot. In medieval England the scot was a tax levied on the members of a village or town which all the inhabitants had to pay in proportion to the size of their property or the extent of their land. Some people avoided the scot, however, often because their houses were built in unfavourable places such as hills with no water or places prone to flooding. Such people were described as scot free and the term has now come to describe anyone who avoids a punishment or financial penalty that they would normally have to serve or pay.