Can be any words used to describe a concept or idea. Keyword search is the most flexible way to research a topic.
meaning of life
Covid-19 and discrimination
pandemic and environment*
climate change and pandemic
civilization and pandemic
science and pandemic
trauma and pandemic
(covid-19 or coronavirus or 2019-ncov)
over-consumption or consumerism
Are "controlled vocabulary" assigned by information organizers to capture a subject. We can discover subject words in the description of a book or article.