Salutary neglect refers to the trade policy created by Prime Minister Walpole for the British Colonies in North America.
In essence, it was a relaxing of trade laws wherein the British Colonies (future US) were allowed to do their own thing without too much interference from London.
The effect was that the American colonies started to largely thrive on their own two feet and felt less of an obligation to the Crown in London. When salutary neglect ended, many bristled and the American revolution began.