Spread
A spread effect extends out like a burst, but it can turn corners. You select the point of origin, and the effect spreads out to a given distance in all directions. The effect can extend around corners and into areas that you can’t see. Calculate distance using the actual distance the effect travels, taking into account turns the effect takes and counting around walls and corners, not through them. You must designate the point of origin for such an effect, but you need not have line of effect (see page 271) to the entirety of the effect’s area.
Source
Core Rulebook pg. 268