Opensource.com - https://opensource.com/article/18/1/history-low-level-container-runtimes
At Red Hat we like to say, “Containers are Linux—Linux is Containers.” Here is what this means. Traditional containers are processes on a system that usually have the following three characteristics:
1. Resource constraints
When you run lots of containers on a system, you do not want to have any container monopolize the operating system, so we use resource constraints to control things like CPU, memory, network bandwidth, etc. The Linux kernel provides the cgroups feature, which can be configured to control the container process resources.