An example of a beatmap that is being marked with the 'explicit' tag.
Mappers are able to declare whether the content of their beatmap is explicit by using a check box in the genre and language popup on the website. This feature has a few expectations and rules governing its use.
Regardless of the nature of the audio, make sure it also complies with the general song content rules.
Explicit content refers primarily to the audio content of a beatmap, mostly in theme, subject matter, or heavy use of explicit language. It does not apply to visual elements of a beatmap—those must adhere to the Visual Content Considerations.**
Generally speaking, most forms of music are acceptable to use in beatmaps with very few exceptions, so long as they are marked appropriately.
Mild (or single) use of any common profanity is not enough to qualify a beatmap for the explicit content marker. Beatmaps with this kind of language can safely be left without being tagged as explicit—so long as the language is what one would reasonably expect from something classified as requiring "parental guidance" (PG-13). If any arguments break out over whether this is relevant for a given track, assume that it is not.
Profanity use must be sustained, significant, heavily inflammatory, or highly repetitive in order to count as explicit.
In addition, vivid and sustained discussion of controversial topics or anything that a reasonable person would consider as "heavy" should be considered as explicit. Some (but not all) examples are:
A good way of discerning if something should be tagged as explicit or not is if any major audio streaming services have it listed as such on their own platforms. Spotify is an excellent place to start.