Docker is releasing Containerd (pronounced container-dee), a set of basic components designed to run containers, as part of an open source project.
Containerd includes supervisor and executor components that work together to function as the core container runtime that underpins the company's Docker Engine software. It's designed to allow companies to build their own software for managing containers while using a consistent foundation.
As the name implies, containers provide applications with a lightweight, constrained environment that makes them easy to migrate, scale up and scale down across different hardware. They've had increasing use over the past year, in part because they make it easier for developers to have a consistent environment for their software.