What does (s) mean in a spell effect?

[LordBiBo]

The spell Wall of Thorns has a parenthetical S in its effect section:

Effect wall of thorny brush, up to one 10-ft. cube/level (S)

What does that (S) mean?

[Val'bryn2]

Shapeable. You can, to an extent, form the wall around things

[Kayerloth]

CRB, Magic wrote:

(S) Shapeable: If an area or effect entry ends with "(S)," you can shape the spell. A shaped effect or area can have no dimension smaller than 10 feet. Many effects or areas are given as cubes to make it easy to model irregular shapes. Three-dimensional volumes are most often needed to define aerial or underwater effects and areas.