A family of Microsoft word processing software products for creating web, email, and print documents.
I assume that it is a caption label that you created, that you now do not want to appear in the Cross Reference dialog.
User defined captions are stored in your Normal.dotm template.
To delete one, go to References>Insert Caption and expand the Label list and select the unwanted Caption and then click on Delete Label and then click on OK.
Note, you cannot delete the default Equation, Figure and Table captions.