The window tax was a glass tax which was a significant social, cultural, and architectural force in the kingdoms of England, Scotland and then Great Britain during the 17th and 18th centuries. Some houses from the period can be seen to have bricked-up windows, as a result of the tax.
Glass making was costly and the use of glass for windows and other purposes was even costlier because of a tax levied specifically on it. The tax was introduced in 1696 under King William III and was designed to impose tax relative to the prosperity of the taxpayer, but without the controversy that then surrounded the idea of income tax. At that time, many people in Britain opposed income tax, on principle, because they believed that the disclosure of personal income represented an unacceptable government intrusion into private matters, and a potential threat to personal liberty. In fact the first British income tax was not introduced until the late 18th century and the issue remained intensely controversial well into the 19th century. Window tax was relatively unintrusive and easy to assess. The bigger the house, the more windows it was likely to have, and the more tax the occupants would pay.
The richest families in the kingdoms used this tax to set themselves apart from the merely rich. They would commission a country home or a manor house whose architecture would make the maximum possible use of windows. In extreme cases they would have windows built over structural walls. It was an exercise in ostentation, spurred by the window tax.
The tax was not repealed until 1851, when it was replaced by a tax akin to the present-day council tax.
Some allege that the term "daylight robbery" originated from this tax, but given that the phrase daylight robbery was first recorded in 1949, many years after the "window tax", this seems unlikely.
The Oxford English Dictionary's (OED) first example of daylight robbery was from 1949. Though the figurative sense has been around a bit longer than the OED says — it appears for example in Harold Brighouse's 1916 play Hobson's Choice.
A similar tax existed in France from 1798 to 1926, the Doors And Windows Tax.