Fizzle is an informal term used to describe what happens when a spell or ability is countered on resolution. It is a flavorful and descriptive term, but what it really means depends on who you ask. Some have used the term to apply to individual effects when resolving a spell or ability. Or when a spell actually does resolve, but doesn’t have an effect on the game. Unlike other terms like ‘summoning sickness’ it is not supported by the comprehensive rules.

So, Fizzle means to be countered on resolution due to the fact that all of the targets the spell or ability had are now illegal. But even then, I recommend not using the term as it is not official and means different things to different players.