This section is from the "Hand Sewing Lessons" book, by Sarah Ewell Krolik. Also available from Amazon: Hand Sewing Lessons: A Graded Course For Schools And For The Home.
Cloth is a woven or felted fabric.
A selvedge is the woven edge of cloth.
A raw edge is one that is cut or torn.
A seam is a line formed to join two pieces of fabric.
A nap is a surface of fine hair or fiber combed from the cloth, and lying smoothly in one direction.
The lengthwise threads are called the warp. It is parallel with the selvedge.
The crosswise threads are called the woof. It runs from selvedge to selvedge.
A bias is a slanting line across warp and woof.
A true bias is one that has the same angle to the warp that it has to the woof.
The warp is nearly always stronger and firmer than the woof, and shrinks more when washed.
The woof usually stretches more than the warp. As woof will stretch, make this test when pieces are to be joined with warps parallel. Cut off selvedge edges when not required, or clip them at intervals.
Cloth sometimes becomes crooked when pressed at a factory. It is straight when you can ravel the torn edges. If it does not seem straight, stretch it diagonally until it is. Cloth tears more easily lengthwise than crosswise. Cloth for hand sewing should be soft, and not too closely woven for the needle to pass through it easily. Cut linen on the line of a drawn thread and ginghams by a thread of the pattern.