Linux cgroups are used to limit, manage, and isolate resource usage of collections of processes running on a system. Resources are CPU time, system memory, network bandwidth, or combinations of these resources, and so on.
Engineers at Google have originally implemented this feature starting in 2006. The cgroups functionality was merged into the Linux kernel mainline in kernel version 2.6.24, which was released in January 2008.
Using cgroups, administrators can limit the resources that containers can consume. With this, one can avoid, for example, the classical noisy neighbor problem, where a rogue process running in a container consumes all CPU time or reserves massive amounts of RAM and, as such, starves all the other processes running on the host, whether they're containerized or not.