warp and woof

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The underlying structure on which something is built; a base or foundation.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The threads in a woven fabric, comprised of the warp (threads running lengthwise) and woof (threads running crosswise) to create a the texture of the fabric.
• noun by extension The fundamental structure of any process or system.