Is it nonboldface? Is bold's antonym nonbold? Is it unemboldened? Is it hyphenated? What word do I use to mean text that is not in boldface style?
Roman is the technical term for non-bold, non-italic.
Bold refers to the weight of a typeface. A non-bold typeface, regardless of any other properties, is called light.
I would call this type of text simple or plain. However, I don't think this is an antonym for boldface. It is just text which isn't bold-faced, italicised or underlined.
Apart from the answers given above, I would like to provide one. A Non-bold type face is often also called as a regular type face.