Sentence:  <WSD>Gerunds</WSD> and <WSD>gerund</WSD> phrases are always nouns, so they are always predicate nominatives when used as complements. Do be careful to distinguish progressive-tense verbs from <WSD>gerunds</WSD> used as subjective complements. 
Meaning of the word marked with <WSD> tags:  A verbal form that functions as a verbal noun. (In English, a gerund has the same spelling as a present participle, but functions differently.)