A gloss (plural glosses), from Greek γλῶσσα ‘language, tongue’, is a word or a phrase that explains a corresponding section in the text, called lemma (λῆμμα, pl. lémmata), usually written above the line or in the margin of the manuscript. Sometimes, a gloss in an older manuscript was introduced in the text of a later manuscript and thus created an interpolation.
In other languages
DE: Glosse (pronounced with a long o)
FR: glose
IT: glossa
OH