Texture is one of the elements of art and design (others include line, shape, form, space, color, value).
In architectural design (and art in general), texture refers to the perceived surface quality of a material or object. It can be:
(^) Tactile (Actual) Texture: The physical feel of a surface when touched (e.g., rough, smooth, bumpy, soft, hard).
(_) Visual Texture (Implied Texture): The illusion of a physical texture created on a surface through visual means (e.g., a photograph of wood grain on a laminate surface, a painted imitation of stone).
The question asks what "Texture" refers to.
Let's evaluate the options:
(`) (a) The visual weight of elements: Visual weight refers to the perceived heaviness or lightness of a design element, influenced by factors like size, color, density, and placement. This is related to visual balance, not directly texture.
(a) (b) The arrangement of colours in a composition: This refers to color theory, color schemes, and how colors are used and combined in a design. This is distinct from texture.
(b) (c) The tactile quality or feel of surfaces: This is the core definition of texture – how a surface feels to the touch (actual texture) or how it appears it would feel (visual texture). Examples: the roughness of stone, the smoothness of glass, the softness of fabric.
(c) (d) The repetition and variation of patterns: Pattern refers to the repetition of design elements (lines, shapes, colors, textures) in a regular or irregular arrangement. While a pattern can be made of textures, texture itself is the surface quality, not the repetition.
Therefore, "Texture" in architectural design refers primarily to the tactile quality or feel of surfaces (and its visual representation).
\[ \boxed{\text{The tactile quality or feel of surfaces}} \]