The "Show converted" toggle in osu!(lazer)
Converts (or converted beatmaps) are beatmaps of a specific game mode that have been "converted" by the osu! client in-game in order to be playable in another game mode they were not originally created for. All converts are automatically generated based on certain parameters present in the base beatmap.
As it stands, osu! supports conversions of beatmaps from the osu! game mode into osu!taiko, osu!catch, and osu!mania.
See also: osu!taiko mapping/osu! conversion notes
osu!taiko converts are generated according to the placement of hitsounds, rhythm, and slider velocity changes in a beatmap. Depending on the type of the hit objects and their corresponding hitsounds, the conversion generally goes as follows:
See also: osu!catch mapping/osu! conversion notes
osu!catch converts are generated according to the rhythm and horizontal placement (e.g. the x-axis coordinate) of the hit objects in a beatmap as follows:
osu!mania converts are generated mostly according to the rhythm of the beatmap, and are supposedly much more random than converts in other game modes. While there is no consensus as to how osu! to osu!mania conversion works precisely, it generally goes as follows:
In addition to the above, osu!mania converts are unique in a sense that the resulting convert can either be 4K, 5K, or 7K depending on the difficulty of the original beatmap.