gerund / present participle
The -ing form as a noun versus the -ing form as a verb or an adjective.
A gerund is the -ing form used as a noun: Filing took an hour. A present participle is the same form used as a verb or as an adjective: She is filing. The filing clerk left. The ending is the same. The job in the sentence is not.
Examples
UseWaiting tired her. (gerund)
UseShe is waiting. (present participle)