if you’re looking at the kernel features used (namespaces, cgroups, etc) containers are multiprocess (even with docker you can go attach into the container and look at things).
This may be semantics, but the first process in the container is an “init” regardless if it’s a proper init or just a process.
As far as light-weight VMs: containers are supposed to be lightweight VMs (But defining lightweight can be challenging)
let's agree to disagree on this one. I am not sure that system and application container are or should be different, but it's okay if we have a different opinion.
This may be semantics, but the first process in the container is an “init” regardless if it’s a proper init or just a process.
As far as light-weight VMs: containers are supposed to be lightweight VMs (But defining lightweight can be challenging)