User blog comment:Fbhuvjhvbnvfdkv hfd/KS - Kill steal or Kill secured?/@comment-4068613-20140520065508

Both of these things exist, and both are regularly misdiagnosed. If a bruiser is having an easy time whittling down their opponent and suddenly the support erupts from the woodwork and pokes for the last hit, that's a kill steal.

In a chaotic teamfight, Sona's spamming all her abilities to make sure the enemy Nidalee doesn't get away and finishes her off with her Q. That's Kill Secured.

It's really only a kill steal if both A) It's clear that the parties involved have it under control, and B) The final hit is really the only contribution the "stealer" gives to the kill.