Windows is the Operating System (OS) developed by Microsoft and designed to run on any X86 class computer hardware. Windows is probably the best known and most widely installed OS - largely due to the deal struck between Microsoft and IBM in the 1980s for Microsoft to produce a GUI type interface to compete with that of Apple's Macintosh machines - as it was designed from the outset to run on any hardware following the IBM structure. Windows is well supported when it comes to Office and creative applications.
Although propriatory, and not itself Free and Open Source (FOS), there are many FOS software applications, such as Libre Office, available for Wndows.
Windows is inherently vulnerable to malicious software and computer virus infection, though versions from Windows 7 on are more secure than earlier versions. This is due, in part, to the predominance of Windows on home and business PCs but also to the the way in which Windows is constructed, using a Registry to allow developers to 'hook' into the Windows OS kernel.
It is essential to run anti-virus software and to allow Windows updates to run regularly when running Windows OS, though the in-built Windows-Defender is adequate for most user's anti-virus/anti-Mal wear needs.