TeX Live is an easy (we hope) way to get up and running with the TeX document production system. It provides a comprehensive TeX system with binaries for most flavors of Unix, including GNU/Linux, macOS, and also Windows. It includes all the major TeX-related programs, macro packages, and fonts that are free software, including support for many languages around the world. Many operating systems provide it via their own distributions.
Some starting points for actually using TeX are in this introduction to the TeX world.
By the way, if you don't care for TeX Live's setup for whatever reason, the major (free software) alternative is MiKTeX, which runs on GNU/Linux, macOS, and Windows.
Plan for TeX Live 2020:
15feb: candidate/final sources committed, test builds begin.
22feb: tlnet (and TL'19) frozen, tlpretest starts, CTAN updates continue there.
15mar: code freeze for final build, major bug fixes only.
22mar: final updates from CTAN, final doc tweaks.
29mar: deliver TL image for TeX Collection packaging/testing.
5apr: deliver TeX Collection DVD image for manufacturing.
10apr: public release (also of MacTeX).
June?: delivery of DVDs to members.
TeX Live has been developed since 1996 by collaboration between the TeX user groups. TeX Live was originally perpetrated by Sebastian Rahtz. Present miscreants include Akira Kakuto, Karl Berry, Luigi Scarso, Mojca Miklavec, Norbert Preining, Reinhard Kotucha, Siep Kroonenberg, and a cast of thousands.