Linux is the name commonly used for quite a few things that are not actually Linux. We are also not talking about Lenox dishes or Lennox climate control. This fact is a key contributor to the difficulty we have in describing "Linux" to others. Linux is the most central part of quite a few operating system distributions. Each of these are made of many different parts.
Our user group, other groups like ours and distributions are often named after the one central part of the operating system called a kernel (wikipedia), the Linux Kernel (kernel.org) begun in 1991 by Linus Torvalds, then a Finnish student of the University of Helsinki. It has grown larger than he ever imagined at that time.
A kernel is the central part of the operating system. It can do very little alone. People want to use computer programs that do things. Hardware and operating systems are means to the end of getting things done. In our fast paced western world people seek out and buy "solutions" sometimes without knowing exactly what problem is solved.
Linux distributions offer people the kernel packaged with many other parts to offer a full operating system. Many of the most important parts are widely acknowledged to come from the Free Software Foundation’s GNU project.
Programs are written to perform their intended tasks or purpose. To do their tasks programs must make their requests for CPU, memory, files and network resources.
The parts of the kernel that work most closely with the hardware are called device drivers. These drivers allow the operating system to use all the hardware capabilities for things like keyboards, mice, video card, hard disk, USB, removable media, network (including Wi-Fi) and power monitoring.