appositive / apposition
A noun phrase that renames another noun, and the commas that mark it.
An appositive is a noun or noun phrase set beside another noun to identify it: my sister, a chemist, the poet Keats. If the appositive is extra information, set it off with commas: My editor, Dana Ruiz, cut the chapter. If it is needed to identify which one, use no commas: the poet Keats my sister Dana. Do not put one comma in and leave the other out.
Examples
UseHer landlord, a retired judge, refused the offer.
UseMy sister Dana called. (She has more than one sister.)
AvoidHer landlord a retired judge refused the offer.