No, it's a Yiddish word meaning chicken fat. It came to mean "stuff" because old-world Jewish cooks would add schmaltz to foods for extra flavor. The traditional way of preparing schmaltz is to take raw chicken fat (including pieces of skin attached to the fat) and cook it with an onion added to the fat as it cooks- the end result isn't just rendered chicken fat, but something with a very distinctive flavor. I don't know if chicken fat would have a milder flavor if rendered without the onion- I've never tried that.
Long before there were commercially available vegetable oils, kosher cooks used schmaltz for cooking meat meals and butter for cooking dairy meals.