What we consider to be straw is grain like wheat or rye that has been harvested. When harvesting, the straw can be scattered or made into a windrow for baling. The only time we bale straw is if there is nothing else to bale and hay is scarce. Nutrition value is poor, but it will help keep the stomach full.
Yup, straw is usually the small grain plant [oats, wheat, barley] after harvesting. They also do some Soy bean straw and grass straw and other crops. All after the seed is taken off. Most widely used for livestock bedding, sometimes used as a poor quality cattle roughage with nutrients added. And very commonly used as mulch along roads etc.