It's a dump of the state of the run-time environment, including data. Probably the easiest use case is using it as a savegame feature when you're working in the

It's a dump of the state of the run-time environment, including data. Probably the easiest use case is using it as a savegame feature when you're working in the REPL. It's not necessarily portable. Some lisps will use machine-independent bytecode, others use native code. I'm not sure which one Janet does.