walled gardens

There are literal walled gardens in the world. These gardens are surrounded by walls to keep out animals, unwanted human visitors and in some places, the walls shelter the garden from wind and frost. They can also be decorative and there may be smaller walls within the walled perimeter. 

A later development was the walled or gated community. One of the primary purposes of a gated community is to offer its residents safety. Some were built near areas that were considered unsafe. Besides having walls, a gated community increases safety by having membership, guards and by eliminating through traffic.

These days if you hear the term there is a good chance that it is a figurative walled garden that is a closed platform or closed technology ecosystem. Since we borrowed the term "ecosystem" from nature and have since created manmade ecosystems (or damaged others), it makes sense that we turn botanical garden ecosystems into technology ecosystems.

A good example of such an ecosystem is Apple’s hardware, software and services which work harmoniously together and do not work with other hardware, software and services. Apple users tend to remain, not always by choice, in their walled garden. This has also led to antitrust scrutiny (note the Epic vs. Apple case. Google, Facebook and others would like to keep you in their walled gardens.