Containerization is an alternative approach to virtualization. In a traditional virtual machine environment, each VM "guest" runs a full copy of the operating system plus its relevant libraries and systems tools on top of a hypervisor. Each workload has its own physical server hardware, which, in turn, necessitates heavy system requirements.
Containerization, by comparison, eliminates the hypervisor, meaning that only the resources needed to run the container are in use when an instance is spun up. Each application deployed in a container environment runs on a single, shared instance on the OS kernel. One benefit is that, for rapid deployment of applications, containers eliminate the need for VMs altogether.