The signature ability of the bard is their battle song. While active, the party will be fortified against fear, both natural and magical. Specifically, the party will be rendered immune to magical fear, will have any such existing effects removed from them and their morale will be gradually restored to its baseline while they hear the song.
Jesters are specialised in ridicule and hilarity and use this to their advantage in combat. The only difference between a bard and a jester is in the Bard Song. Instead of aiding allies, it affects opponents in area of 30 feet, who must make a save vs. spells at +4 each round or they get confused.
Bard Song has different effects depending on the level of the skald. At level 1, it gives allies -2 THAC0 and +2 damage. At level 15 it gives allies -4 THAC0 and +4 damage and immunity to fear. At level 20, it adds immunity to stun and confusion as well.