The END symbol tells the player where to finish. On the last chorus the player holds the first chord of the marked bar under a fermata, instead of playing through to the end of the chart.

 

Add it from the Symbols button in the Editor, and tap or click END again to remove it. A fermata on its own is decorative, and the player ignores it.

 

There is no fade out or ritardando in the player.

 

For the full guide, see Edit a song on the iReal Pro website.