It's not really a standalone file format, it's executable Lua code.
It returns a new item with the given table contents.
That syntax with the keys in square brackets is the "long-form" method of creating a new table, that's allows the use of spaces and dashes in the key name.
assuming you run it in the right lua environment. The item function must be defined, and we're only speculating about its return value without seeing proper docs, or the source
the code is constructing a table, and passing it to a function called item. But if all you need is the data, you can just remove the function call and assign the table to a variable like so: local myvar = {...}.