Windex is the name of a specific brand of window cleaning product that is manufactured by S.C. Johnson & Son which consists largely of ammonia, detergent, and varying colors of dye. The Windex brand also includes cleaners for non-glass surfaces, although it is most widely associated with windows.
Here's some more information about what Windex is and why it can be beneficial in cleaning your home, as well as some important points to keep in mind when using it.
Windex dates back to 1933 as an invention of Erich Drafahl. The original Windex had to be sold in metal cans and was highly combustible, but it was reformulated after its first decade, and the formula has continued to be tweaked into the product we know and use today. The product Windex is today manufactured by S.C. Johnson and Son, which acquired it in 1993. Since the invention of Windex, many generic knock-offs and imitators have also been made available -- and sometimes the term "Windex" is used generically to refer to any type of glass cleaning product, similarly to how some people say "Kleenex" for any type of facial tissue regardless of brand.
The formula of Windex includes ammonia as a main ingredient, which is what gives Windex its familiar strong odor. The product also contains smaller amounts of alcohol, as well as detergents for added effectiveness and solvents for stability. Some products also contain fragrances. Traditionally Windex also has a bright blue dye added, which gives it a characteristic and widely recognized color. Many generic knock-offs of Windex attempt to imitate this color.
Windex (or a generic imitator) is generally the top choice for cleaning windows or glass surfaces because the ammonia and other ingredients cause Windex to be able to clean glass without leaving visible streaks. A standard cleaner used on glass can make the glass clean, but when it dries, the glass will be left with streaks following where the cloth was used to wipe the glass. This can be unsightly on windows, mirrors, and similar surfaces. With Windex the cleaning is equally effective and often more so, and no streaks are present when the cleaner has dried. Note that attempting to use Windex on very hot or cold surfaces can lead to the Windex evaporating before it has a chance to dissolve the dirt, so it is best to use it on room-temperature items.
The movie "My Big Fat Greek Wedding" included a character who believed that Windex was able to solve a host of skin problems ranging from acne to baldness. Since then, there have been various stories on the Internet of people testing Windex as a cure for different ailments, some claiming that it actually works. Theoretically Windex may work as an antibacterial agent, but trying to use Windex for anything other than cleaning your home is at your own risk. If you have skin ailments, it is best to speak to a doctor and use medications intended for use on skin rather than attempting to heal yourself with window cleaning products.
Windex can irritate your eyes and respiratory system, so use appropriate precautions when using it. If the smell bothers you, consider airing out the room in which you are cleaning. And like with most other cleaning agents, Windex should always be kept out of the reach of children and pets -- and call Poison Control or 911 immediately if accidental ingestion occurs. Also, be careful before using Windex on tinted windows as it may be inappropriate for some window compositions. (Test it on a small area when in doubt.)