Content gap analysis is a comparison of your own website with competitors to find queries and topics for which competitors rank and you do not. It is carried out by downloading the queries of several genuine competitors in an analytics tool, filtering out branded and irrelevant ones, and comparing the remainder with your own coverage. The result is a list of opportunities ranked by query value and by how close the topic is to the company's offering. The same approach can be used to compare coverage within a single topic, that is, which sub-questions competitors cover and you do not. The analysis does not need to be done often, but when preparing the content plan for the next period it saves a lot of debate about what to write about.
See also: Content audit, Competitive analysis, Semantic topic coverage.