A capo is a device used to shorten the playable length of the strings on a guitar, effectively raising the pitch. In the context of the ChordU app, the Capo feature digitally emulates the use of a physical capo. It allows you to simulate the effect of placing a capo on a specific guitar fret without needing the physical device.
The utility of the Capo feature in ChordU is that it enables you to play a song in a different key without learning new chord shapes or manually transposing the chords. The app automatically adjusts the displayed chords by selecting the desired fret position on the virtual capo. This makes it easier for guitarists to play along with songs or adjust the key to match their vocal range.