To get off scot free means to escape without punishment - scot free (originally 'skot free') meant 'free of taxes', particularly tax due from a person by virtue of their worth. One who avoided paying their tax was described as 'skot free'. 'Scot and lot' was the full English term for this levy which applied from 12th to 18th century. Scot was derived from the Norse 'skot', meaning tax due from a tenant to his landlord; 'lot' meant the amount allotted. Less significantly, a 'skot' was also a slate in Scottish pubs onto which customers' drinks debts were recorded; drinks that were free were not chalked on the slate and were therefore 'skot free'. In the USA, the expression was further consolidated by the story of Dred Scott, a slave who achieved freedom, presumably towards the end of the slavery years in the 19th century, by crossing the border fom a 'slave state' into a 'free state'

The origin of this phrase dates back to the thirteenth century. “Scot was the word for money you would pay at a tavern for food and drink, or when they passed the hat to pay the entertainer. Later, it came to mean a local tax that paid the sheriff’s expenses. To go scot-free literally meant to be exempted from paying this tax.” (From the book How Does Olive Oil Lose its Virginity?, by Bruce Tindall and Mark Watson)

O.E. scotfreo "exempt from royal tax," from scot "royal tax," from O.N. skot "contribution, reckoning, shot" + freo (see free). Related to O.E. sceotan "to pay, contribute," Du. schot, Ger. Schoß "tax, contribution" (see shot). O.Fr. escot (Fr. écot) "share" is a Gmc. loan-word. http://www.etymonline.com/index.php?term=scot-free Meaning To escape pursuers or avoid payment. Origin Dred Scott was a black slave born in Virginia, USA in 1799. In several celebrated court cases, right up to the USA Supreme Court in 1857, he attempted to gain his freedom. These cases all failed but Scott was later made a free man by his 'owners', the Blow family. Knowing this, we might feel that we don't need to look further for the origin of scott free. Many people, especially in the USA, are convinced that the phrase originated with the story of Dred Scott. The etymology of this phrase shows the danger of trying to prove a case on circumstantial evidence alone. In fact the phrase 'scot free' has nothing to do with Dred Scott. Given the reputation of Scotsmen to be careful with their money we might look to Scotland for the origin of 'scot free'. Wrong again, but at least we are in the right part of the world now. A scot is a Scandinavian word for tax or payment. It came to the UK as a form of redistributive taxation which was levied as early the 13th century as a form of municipal poor relief. The term is a contraction of 'scot and lot'. Scot was the tax and lot, or allotment, was the share given to the poor. Scot as a term for tax has been used since then to mean many different types of tax. Whatever the tax, the phrase 'scot free' just refers to not paying one's taxes. No one likes paying tax and people have been getting off scot free since at least the 16th century. This reference from Vincent Skinner's translation of Reginaldus Gonsalvius Montanus's A discovery and playne declaration of sundry subtill practises of the holy inquisition of Spayne dates from 1598: "Escape scotte free." http://www.phrases.org.uk/meanings/scot%20free.html The "scot" in question comes from the Old English word "sceot," meaning a tax or penalty. As long as there have been taxes there have been tax evaders, and anyone who managed to avoid the tax collector got away "scot-free." Gradually the term came to mean one who escapes any rightly deserved payment or punishment. http://www.word-detective.com/122099.html#scotfree Scot is from an Old Norse word that meant a payment or contribution and which is linked to the modern French écot, a share of communal expenses, as in payer son écot, to pay one’s share. It is a close relative of shot, which at one time could have the same meaning of a contribution or a share of expenses. The expression scot free derives from a medieval municipal tax levied in proportional shares on inhabitants, often for poor relief. This tax was called a scot, as an abbreviation of the full term scot and lot, where scot was the sum to be paid and lot was one’s allotted share. (This tax lasted a long time, in some places such as Westminster down to the electoral reforms of 1832, with only those paying scot and lot being allowed to vote.) So somebody who avoided paying his share of the town’s expenses for some reason got off scot free. http://www.worldwidewords.org/qa/qa-sco1.htm

I think its when you have unprotected sex and don't get pregnant.