Salutary neglect refers to the British policy of allowing the colonies in America to essentially self-govern during the 17th and 18th centuries free from excessive enforcement of parliamentary laws and regulations. It was established as an unofficial and unwritten policy in the early 1600's with the expressed belief that giving the colonies semi-autonomy would allow them to flourish economically which would be of benefit to the empire through trade and mercantilism.
One such example is the passing by Parliament of the Navigation Acts which in 1651 were established to prevent trade by any members of the British Empire or related kingdoms with outside countries or entities. The British Empire wanted to keep all of the gold and silver that they had mined in their various imperial outposts around the world within their friendly territories and hoped to keep all trade internal to accomplish this. This rule was not heavily enforced with the American colonies and they were allowed to trade freely with any entity that was willing to pay for their goods, often times with countries that were on unfriendly terms with the English crown.
Light enforcement of laws such as the Navigation Acts coupled with the long standing tradition of the colonies' self-governance through their democratically elected legislatures gave the colonies a sense of individuality and sovereignty away from the empire. After the Seven Years' War, Britain gained a large amount of new territory in America and attempted to reign in control on the continent both with the new territories and the established colonies. This move for control was viewed by the colonists as hostile after such long standing traditions of self-governance and the passing of the Stamp Act, Sugar Act, and other "Intolerable Acts" would eventually lead to the colonists declaring their independence in 1776. The attitudes that contributed to this declaration would have been much more difficult to establish had the British Empire enforced their rule of law from the creation of the colonies.