The Linux kernel is the heart of the Ubuntu operating system. A kernel is an important part of any operating system, providing the communication bridge between hardware and software.
Linux was brought to life in 1991 by a Finnish student named Linus Torvalds. At the time, it would run only on i386 systems, and was essentially an independently-created clone of the UNIX kernel, intended to take advantage of the then-new i386 architecture.
Nowadays, thanks to a substantial amount of development effort by people all around the world, Linux runs on virtually every modern computer architecture.
The Linux kernel has gained an ideological importance as well as a technical one. There is an entire community of people who believe in the ideals of free software and spend their time helping to make open source technology as good as it can be.
People in this community gave rise to initiatives such as Ubuntu, standards committees that shape the development of the Internet, organizations like the Mozilla Foundation, responsible for creating Mozilla Firefox, and countless other software projects from which you've almost certainly benefited in the past.
The spirit of open source, commonly attributed to Linux, is influencing software developers and users everywhere to drive communities with common goals.