No. It's a common enough term, but the handwavy concept I wanted to get across is that if you have code mixing and matching different syntaxes then there will necessarily be boundaries between those. Code with one syntax (if you can actually mix and match runtimes as the comment author said they want) will behave differently from "adjacent" (commonly a different file or directory, but I could imagine multiple syntaxes within a file too) code with a different syntax.
In common languages, you're usually still targeting the same runtime in different compilation units, but it's a rough description of optimization boundaries (you compile one unit at a time and stitch them together during linking). Some techniques bridge the gap and thus the language crispness (e.g., post-hoc transformations on compiled units, leading to one larger "effective" compilation unit), but you can roughly think of it as equivalent to a whole shared library.
In common languages, you're usually still targeting the same runtime in different compilation units, but it's a rough description of optimization boundaries (you compile one unit at a time and stitch them together during linking). Some techniques bridge the gap and thus the language crispness (e.g., post-hoc transformations on compiled units, leading to one larger "effective" compilation unit), but you can roughly think of it as equivalent to a whole shared library.