Here's why:

* Foliation refers to the parallel alignment of minerals within a metamorphic rock. This alignment is caused by pressure and heat during the metamorphic process.

* Gneiss forms under high pressure and heat, causing its minerals (often quartz and feldspar) to recrystallize and align in bands or layers. These bands are the defining characteristic of gneiss's foliation.

While the banding in gneiss might look more like layering than the thin, flat sheets often seen in other foliated rocks like slate or schist, it is still a form of foliation.