What does "gloss" mean in writing?

In writing, editing, and literary studies, gloss has a very specific meaning that is different from its everyday meaning of shine. A gloss in writing is a brief explanation, definition, translation, or commentary on a word, phrase, or passage that might be difficult, archaic, technical, or in a foreign language. In ancient and medieval manuscripts, scribes would write glosses between lines or in the margins to help readers understand the main text without altering it. This practice is called glossing. For example, if a medieval copy of the Bible had a difficult Hebrew word, a monk might add a small Latin explanation above it, that explanation is the gloss. A collection of such explanations is called a glossary, which we still use today at the end of textbooks. In modern writing instruction, to gloss a text means to annotate it with helpful notes. As a verb, to gloss can also have a negative sense in writing, to gloss over something means to treat a complex issue superficially, to minimize it, or to explain it away without adequate depth. So in writing, gloss means either a helpful explanatory note or, in its negative form, a superficial covering up.