Sentence:  Backing for the plywood is provided by 2” × 12” wooden planks (<WSD>"walers</WSD>" in forming technology) spaced approximately 15 inches apart in the vertical direction and running the full length of the wall section. The form ties are ¾-inch pipe clamps, spaced 6 to 10 feet apart in the horizontal direction. In the typical concrete forms, <WSD>walers</WSD> are 2×4's and form ties are spaced at 2-foot intervals. By using 2×12 <WSD>walers</WSD>, form ties can be spaced at up to 10-foot intervals. 
Meaning of the word marked with <WSD> tags:  A plank of wood, block of concrete, etc., used for support or to maintain required separation between components in order to help maintain the form of a construction under stress.