Linux is a Unix-like operating system, originally designed by Linus Torvalds, for the x86 platform. It has since been ported to nearly every platform. It is freely available with paid support available for enterprise and commercial users.
The Linux operating system comes in different distributions. Popular distributions include Ubuntu, Linux Mint, Debian, Fedora, CentOS, Red Hat, OpenSUSE, SUSE Linux Enterprise, Arch Linux, Slackware, Puppy Linux, and many more. Do NOT ask us what the "best" distribution is, any of the major dists should be fine for you to try.
The main differences between the various distributions are the formats of the software packages, the package maintenance programs, and minor directory structure changes.
For windows users WSL2 supports most major distributions and is an excellent entry into Linux without need to partition or run LIVE USB based distros
Mac users already have Unix/Linux like functionality built in. For package management look into Brew or MacPorts.
Embedded options are also available such as the Android operating system and Debian, Raspberry Pi OS, Fedora, Raspbian, Arch, or Slackware for Raspberry Pi.