Other is a catch-all category for anything that doesn't fit into the other categories on your storage device. When you check how much storage you have available and see other, it can be frustrating because you don't know what is taking up space.
Other usually includes cached data from apps, temporary files, system logs, and other miscellaneous files. Cached data is stored so that it can be quickly accessed again without having to be downloaded from the internet or generated anew each time. Temporary files are just that - temporary. They're created when an app is working on something and then deleted when no longer needed. System logs are created by the Android operating system to keep track of what's going on behind the scenes; they can be useful for diagnosing problems but aren't generally necessary for everyday use. Finally, other miscellaneous files include things like downloads that haven't been moved to their final location yet, orphaned files left over after uninstalling an app, and more.
While other can be frustrating because it's not specific, there are some ways to get rid of unwanted files and free up space. For example, you can clear your cache (which may help if your device is running slowly), delete temporary files (which won't affect normal app operation), or uninstall apps you no longer use (which will also remove any associated orphaned files). If you want to get really granular, there are even apps that will show you exactly what's taking up space in the other category so you can decide what to do with it.