The underlying structure or foundation of something, as in He foresaw great changes in the warp and woof of the nation's economy. This expression, used figuratively since the second half of the 1500s, alludes to the threads that run lengthwise (warp) and crosswise (woof) in a woven fabric.

The essential foundation or base of any structure or organization; from weaving, in which the warp — the threads that run lengthwise — and the woof — the threads that run across — make up the fabric: “The Constitution and the Declaration of Independence are the warp and woof of the American nation.”