A hit is an attack. There are three different types. A successful hit (known as Bleed), either on you or on whatever you are attacking, is denoted by red blood and a red number showing how many Hitpoints the attack caused you/it to lose. A hit that was successfully blocked by a shield or has failed, for example by missing the target, is shown as a Puff (a cloud). Yellow lines known as a Spark occur when the damage was absorbed by an armor or elemental immunity. The three possible effects of a hit are listed here:
However Magic Damage will never "poof". It may only "spark" when absorbed by elemental immunity. Runes, Rods and Wands all deal magic damage.