Linux Containers (LXC) are a way to run System containers on Linux systems. LXC uses kernel features such as cgroups, namespaces and chroot to provide isolation from the rest of the system while sharing the same kernel and eliminating the need of virtualize the host hardware.
LXC is not really meant to be used directly by humans, as it provides only the lower level tools to create containers, but not to manage them in a sane way. Most of the cases we use LXD or Incus to create and manage LXC containers for us. By using those higher level tools we get nice features to manage containers such as projects, profiles and even clustering.
References
Linux Container (LXC) Introduction
https://documentation.ubuntu.com/lxd/en/latest/explanation/instances/