What it actually is
Two proteins in wheat, glutenin and gliadin, hydrate and then link together under mechanical work into a viscoelastic network. Glutenin gives strength and elasticity, gliadin gives flow and extensibility. The balance between them decides whether a dough resists or relaxes, and the network is what traps the gas that makes volume.
Why it matters
Everything a baker judges comes from it: volume, crumb structure, bite, and how the product behaves on the line. Its absence is the entire problem of gluten free baking, where the structure has to be rebuilt from materials that do not naturally form a network.
What changes it
Flour protein quality and quantity, hydration, mixing time and intensity, resting time, and oxidising or reducing agents. Overmixing breaks the network as surely as undermixing fails to build it.
