Sentence:  <WSD>Trope</WSD> theory, though a minority view today, has been popular at various times throughout the history of philosophy, especially among medieval philosophers. <WSD>Trope</WSD> theory holds that properties and relations are themselves (unrepeatable) particulars. (<WSD>Tropes</WSD> are also called 'abstract particulars' – 'abstract' in the sense of fine, partial and diffuse, not in the sense of outside space and time.) Thus the redness of a particular billiard ball is a <WSD>trope</WSD>, located where the ball is and nowhere else. A different but exactly resembling billiard ball has a numerically different but exactly resembling redness <WSD>trope</WSD>. There is no colour property common to, or instantiated in, both balls (similarly all other properties and relations). 
Meaning of the word marked with <WSD> tags:  A particular instance of a property (such as the specific redness of a rose), as contrasted with a universal.