It's the six-meter AoE that Venomous Smite causes.
It lasts 10 seconds, ticks damage once per second, (also can stack with the Bow skill: Poison Injection).
You move with the six-meter Aoe stuck to you (PvP, Battlegrounds, etc.) and affects anybody or any mob in that big green circle.
I was introduced to Venomous Smite in Battlegrounds. Now, heh, I introduce others to Venomous Smite. Vigor and/or Purge would be helpful in coping with it.
~ PS NA ~ ALDMERI DOMINION ~
IVY GOLDBLADE, WOOD ELF NIGHTBLADE, Former Empress
By the way -- both Venomous Smite (procs on hitting someone with a crit) and Poison Injection last 10 seconds and can really eat you up unless you are a tank, for example.
Since my Wood Elf NIghtblade (Dual Wield, Two-Hand, Bow) has racial Poison Resistance the effect is lessened. That Wood Elf racial is helpful in PvP.
~ PS NA ~ ALDMERI DOMINION ~
IVY GOLDBLADE, WOOD ELF NIGHTBLADE, Former Empress
It's a good set - I run it with Defiler on two chars (Warden and Stamplar). On the stamplar its also with Maarselok, great fun and very good for PvE as well.