Dear CMSI, I work for a nonprofit organization that fights racial inequality in public education. I am creating a video about the organization to go in the "About" section on our website, and I want to use a popular song in the background. Would my video qualify as fair use?
The key thing to remember here is that for the use of copyrighted material to be considered fair, the use must be a transformative use of that material. (In other words, it doesn’t have to transform anything in the material itself, but the context of use has to be different.) If the music in your video is only meant to make your video more appealing or emotional, you probably need to find another song. There are a lot of good non-copyrighted songs online that you can use to set a tone. FreeMusicArchive.org might be a good place to start.
But if the song changes the meaning of the other elements of your video, or vice versa, your video may fall under Principle 6  of the Code of Best Practices in Fair Use for Online Video : Quoting in order to recombine elements to make a new work that depends for its meaning on (often unlikely) relationships between the elements. This principle applies to videos that combine media to produce new meanings.
However, the second key thing to remember is that a use is only fair if you only use as much of the material as is necessary for transformative purposes. That means that if there is a particular verse of the song that contributes to the point you’re making in the video, fair use only applies to that verse, not the entire song.
Finally, if you do end up using all or part of the song, make sure you credit it somewhere in your video.
It’s good that you’re thinking about fair use and trying to apply it correctly. These guidelines and the Code of Best Practices in Fair Use for Online Video  should help you decide what qualifies as fair in the future.