A binder is a substance that may be added to foods to thicken or improve texture.
In cooking, binding agents that set when heated include proteins that coagulate such as egg, gluten in flour and blood. Other binding agents set when cold, such as agar-agar, gelatine and starch jellies.
Care must be taken not to use too much of any binding agent as this will result in tough and heavy results. Always use the minimum needed too accomplish the desired result.