Usually I use the localized names when game mechanics are referred to, but I can't make it work with Hibiki's definition, so I just transliterated the original Japanese name instead.
It describes a brief flash of light or a sudden flash of inspiration that comes to the mind momentarily. If activated, it gives you a guaranteed chance of evading the next (and only the next) attack aimed towards you.
The SRW Spirit command is associated with the Newtype flash, hence its name.