Why is it called lye soap?

Lye is the ingredient when added to oils or fats that actually makes soap, soap. I’s chemical name is sodium hydrixide. It was first discoved in volcanic ash . As water ran through and over the ash, it then mixed with fats and turned sudsy. This was the birth of the cleaning agent we call soap. Early colonists would run water through wood ash to get lye and then mix it with tallow or lard to make soap. Sounds like that smelled yummy. So when someone refers to lye soap they are referring to soap their greta grandparents made.