Most textures can be used on both entities and world brushes, though there are cerain restrictions on certain ones.
ORIGIN is always used as part of an entity, it's the point on which a rotating item moves.
CLIP cannot be part of entities. It blocks player movement and is transparent.
{textures with blue are used with a func_wall or other SolidEnt with rendermode Solid and RenderAmt 255, which makes the blue transparent.
{textures with white are used with infodecals. and appear in game as one color, not greyscale.
SKY makes sky and cannot be an entity.
-0, -1, etc. are randomly tiling.
+a, +0, etc are animated.
! is liquid.
~ are light emitting textures.