The term "walled garden" once only meant a literal garden that was enclosed by walls. Though I tagged this post as "tech" and "Open Everything," this topic is not about things being open at all - which of course is a topic of those who discuss openness.
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. These days if you hear the term there is a good chance that it is a figurative walled garden which is a closed platform or closed technology ecosystem. Since we borrowed the term "ecosystem" from nature and have since created manmade ecosystems (or damaged natural ones), it makes sense that we turn botanical garden ecosystems into technology ecosystems.
A tech walled garden is a closed platform or closed technology ecosystem which is a software system wherein the carrier or service provider has control over applications, content, and/or media.With that control, they can restrict convenient access to non-approved applicants or content.
We contrast this with an open platform, wherein consumers generally have unrestricted access to applications and content.
Whether on the broader Internet or a smaller network, a walled garden is a restricted section that only approved users can access. I first encountered this in the earliest days of the Internet with the walled garden of the school nework where I taught. Their server granted access only to students and staff and even that larger walled garden had smaller walled sections withing delegated only to faculty or administration.
It all sounds like something safe - maybe even comfortingly safe. A walled garden can also refer to a closed or exclusive set of information services where a user is unable to leave the closed environment without the owner giving limited points of entry. One example of this comes from Apple’s hardware, software and services work. They work well together as long as you use Apple's devices and services. (see this Wall Street Journal video report)
The Apple walled garden is so closed that it has been targeted for antitrust scrutiny. The recent Epic vs. Apple case is an example of that. The Fortnite video game developer made the case that Apple's walled garden is a monopoly that forces developers to use Apple's in-app purchase system, which gives Apple a 30% cut of all sales.
Walled gardens - literal and figuartive, botanical and technological - have their purposes and will continue to exist, but it is very nice to see gardens and tech ecosystems that are open too.