In computing, you have heard of containers. There are many types. Where can you find a disambiguation of containers?
For SQL Server
In SQL Server for over 10 years, there have been "Foreach Loop Containers". It is a built-in control flow for SQL Server Integration Services. To read more see this Microsoft page.
For Apache Web Server
In Apache Web Server, a container is a portion of configuration code. Filesystem Containers look like this:
<Directory "/var/web/dir1"> Options +Indexes </Directory>
(The above was taken from https://httpd.apache.org/docs/2.4/sections.html.)
Python's built-in containers include dict, list, set, and tuple. according to https://docs.python.org/3/library/collections.html. The previous link explains the different "container datatypes" also known as collections that are commonly used in Python.
For Emulation like Docker, LXC, rkt
In modern computing, emulation containers such as Docker are exceedingly popular. This type of container is a portion of an operating system isolated (via cgroups and namespaces) from other portions of the operating system. In some cases a container's runtime engine is not the same as its host; in these cases it is not a portion of the underlying operating system but an emulation of another operating system. Microsoft defines a container as follows "A standard package of software—known as a container—bundles an application’s code together with the related configuration files and libraries, and with the dependencies required for the app to run." (Taken from https://azure.microsoft.com/en-us/overview/what-is-a-container/#overview.)
Docker defines a container as "A container is a standard unit of software that packages up code and all its dependencies so the application runs quickly and reliably from one computing environment to another." (Taken from https://www.docker.com/resources/what-container.)
A container empowers immutable infrastructure, dependency management, and rapid development and testing while potentially reducing licensing costs (as virtual servers would require additional licenses). LXC, LXD (newer than LXC), and rkt are other types of containers.