If you put bread in a toaster and it becomes overcooked, turning dark or blackened, you technically burned the toast. The term "toast" refers to bread that has been heated to the point of browning or charring through the Maillard reaction, which is a chemical reaction between amino acids and reducing sugars in the bread. This reaction produces a range of complex flavors and characteristic brown color.
So, when you put bread in a toaster, and it becomes too dark or black due to overcooking, it transforms into toast, and you can say that you burned the toast. However, it's essential to keep an eye on the bread while toasting to avoid excessive browning or charring, as it can lead to an unpleasant taste and potentially release harmful substances if the bread is severely burnt.