Windows-1252 or CP-1252 (code page 1252) is a single-byte character encoding of the Latin alphabet, used by default in the Legacy system components of Microsoft Windows in English and some other Western languages (other languages use different default encodings).
It is probably the most-used 8-bit character encoding in the world. , 0.7% of all web sites declared use of Windows-1252, but at the same time 3.8% used ISO 8859-1, which by HTML5 standards should be considered the same encoding, so that 4.5% of web sites effectively used Windows-1252. In addition most web browsers will correctly render it if encountered in text that claims to be UTF-8, so its actual usage may be higher.
It is very common to mislabel Windows-1252 text with the charset label ISO-8859-1. A common result was that all the quotes and apostrophes (produced by "smart quotes" in word-processing software) were replaced with question marks or boxes on non-Windows operating systems, making text difficult to read. Most modern web browsers and e-mail clients treat the media type charset ISO-8859-1 as Windows-1252 to accommodate such mislabeling. This is now standard behavior in the HTML5 specification, which requires that documents advertised as ISO-8859-1 actually be parsed with the Windows-1252 encoding.
Historically, the phrase "ANSI Code Page" was used in Windows to refer to non-DOS encodings; the intention was that most of these would be ANSI standards such as ISO-8859-1. Even though Windows-1252 was the first and by far most popular code page named so in Microsoft Windows parlance, the code page has never been an ANSI standard. Microsoft explains, "The term ANSI as used to signify Windows code pages is a historical reference, but is nowadays a misnomer that continues to persist in the Windows community."
In LaTeX packages, CP-1252 is referred to as "ansinew".
According to the information on Microsoft's and the Unicode Consortium's websites, positions 81, 8D, 8F, 90, and 9D are unused; however, the Windows API [https://msdn.microsoft.com/en-us/library/windows/desktop/dd319072%28v=vs.85%29.aspx MultiByteToWideChar] maps these to the corresponding C1 control codes. The "best fit" mapping documents this behavior, too.