There aren't is the thing. There are widely used standards, but they don't actually have any real basis. Fisher I believe is the one who popularized it but it was for specific circumstances and he acknowledged that it was just a convenient thing.
Sure there are. You can't just call a result "significant" at will. You can pull numbers out of thin air, pre-filter your data or carefully pick a statistical test to be in your favor. But it's still well-defined which outcomes you're allowed to call significant and which ones you can't.