A fizzle is a phenomenon in a Nanovor battle which occurs when the Nanovor suddenly no longer has the EN required to perform a move, and is forced to do nothing. It is functionally identical to a Pass; the Nanovor does not act and instead stockpiles EN.
Here's an example:
Let's say there's a Tank Walker 1.0 facing off against a Gigastriker 1.0.
The Gigastriker has 2 EN, and the Tank Walker 3.0 has 3 EN.
Since Gigastriker 1.0 is faster, it uses Meltdown, dealing minimal damage and subtracting 1 EN from Tank Walker.
Tank Walker 1.0 selected Tank Gore because it had 3 EN at the start of the round, but because of Meltdown, it only has 2 EN, and cannot use Tank Gore, and instead fizzles.