How does "explaining" function in this sentence?

Native speaker’s answer
Rebecca
"Explaining" here is a gerund, which is an "-ing" verb that functions as a noun. It's used here to express that the video explains the origins of a particular expression, and can be replaced by "that/which explains" without changing the meaning of the sentence. Ex: We made a video explaining what vaccines are. = We made a video that explains what vaccines are.