scholium
noun
scho·li·um ˈskō-lē-əm 
plural scholia ˈskō-lē-ə or scholiums
or scholiums 1
: a marginal annotation or comment (as on the text of a classic by an early grammarian)
2
: a remark or observation subjoined but not essential to a demonstration or a train of reasoning
Word History
Etymology
New Latin, from Greek scholion comment, scholium, from diminutive of scholē lecture
First Known Use
1535, in the meaning defined at sense 1