Cast Speed is the term used to describe how fast a player is able to cast a spell. By default, players have 100% cast speed, but this amount can be lowered by various spells, passives, buffs, and equipment. Cast speed is not to be confused with Cast Time, which is how long a spell takes to cast. Cast speed does not affect channeled abilities.
For example: The spell Flamebolt has a default cast time of 1 second. A player with 100% cast speed will take 1 second to cast the Flamebolt, or 100% of 1 second. However, a player with 90% cast speed will only take 900 milliseconds to cast Flamebolt, or 90% of 1 second.
It is beneficial for casters to have lower cast speeds, as this can increase their damage output or increase their healing output since they are able to fit more spells into a shorter amount of time.
Cast Speed Modifiers:
Startling Strain in Songcraft decreases the caster's cast speed by 20% for 5 seconds.
Hummingbird Ditty in Songcraft decreases the caster's or an ally's cast speed by 6-8% for 30 minutes.
Uptempo (Passive) in Songcraft decreases cast speed by 5%.
Inspired (Buff) decreases cast speed by 8% per stack.
Mana Flurry (Passive) in Sorcery decreases cast speed by 6%.
Folding Time (Passive) in Witchcraft decreases cast speed by 4%.
Augment Witchcraft (Passive) in Witchcraft decreases the cast speed of Insidious Whisper by 0.5 seconds.
Alms (Passive) in Vitalism decreases cast speed by 6%.
Wearing full cloth armor decreases cast speed by 4%.