Bean sprouts are the sprouts of mung beans. They are widely available. They are available in pre-packed bags and a la carte. It seems that in the East Coast, they're smaller and don't keep long in the fridge, while on the West Coast, they are bigger and keep longer.
In Thailand, the tiny root that is hanging at the end of the sprout is picked off. It is a tedious job. But every family does it. That is not for me. Too time consuming!