In Dungeon Boss there are two ranges for attacks: Melee and Ranged attacks.
In the description of Abilities the attack range is mentioned together with the damage type. For example 
Willow Swift's 
Sniper Shot is "Critical Armor-Piercing Ranged Physical attack that purges 1 Buff.".
In Melee attacks, the attacker jumps on the target, strikes the blow and jumps back again. There is a danger that so-called skin buffs (or skin passives) on the target or its 
Runes will add a Debuff to the attacker, causing damage or weakening the attacker. Known skin buffs (passives/traits) are 
Poison Skin and 
Disease Skin. See Effects/Debuff, cateogry Skins for a detailed list.
In addition, Melee attacks carry the risk of 
Revenge Attacks, where the opponent immediately switches to counterattack.
Ranged attacks do not have this risk. The attacker, often a mage or archer, stays in his place and performs his attack from there. Ranged attacks have the disadvantage that they are sometimes easier to dodge or some of the damage caused is thrown back to the attacker. Retaliation attacks usually only occur with Ranged Physical (Damage) attacks.