The Comprehensive TeX Archive Network, CTAN, is the TeX and LaTeX community’s repository of free material. It is a set of Internet sites around the world that offer material related to LaTeX for download. Visit CTAN on the web at https://ctan.org.
This material is organized into packages, discrete bundles that typically offer some coherent functionality and are maintained by one person or a small number of people. For instance, many publishers have a package that allows authors to format papers to that publisher’s specifications.
In addition to its massive holdings, the ctan.org web site
offers features such as search by name or by functionality.
CTAN is not a single host, but instead is a set of hosts, one of which is the so-called “master”. The master host actively manages the material, for instance, by accepting uploads of new or updated packages. For many years, it has been hosted by the German TeX group, DANTE e.V.
Other sites around the world help out by mirroring, that is, automatically syncing their collections with the master site and then in turn making their copies publicly available. This gives users close to their location better access and relieves the load on the master site. The list of mirrors is at https://ctan.org/mirrors.