Imagine you want to check out the hypothetical language Jagoust. This goes something like so - you install Jagoust and maybe some Jagoust tools. You fire up your interactive environment and set it up so it knows where Jagoust and its tools are. Using your enviornment you do things like tell Jagoust where your project is or which particular version of Jagoust to use, etc.. And that's pretty much it and while the details are different, the process is quite familiar to you since it just leverages your standard interactive environment in ways mechanically similar to Rugoja, another language you know.

Later you decide you want to try the language Snek. The first thing you notice in the Snek tutorial is that your standard interactive environment is somehow not good enough - you need a meta-environment for it and your project. Perplexed, you google some more docs and ask some Snek people and find out that meta-environment used to be how things were done but these days, you probably want a quasi- or para-environment. But why do you need an environment for your environment? You do not know. Such are the mysteries of the Snek.