Gluten is the component of flour that gives kneaded dough its strength and elasticity. Gluten is a mixture of proteins and comprises most of the protein in flour.  It is easy to extract from flour by washing away the starch.

Mix, then knead, 200g of flour and 120ml of water to make dough.  Then wash the starch away by kneading the dough, with both hands, under under running water from a tap. Initially it will be crumbly and and tend to fall apart, but as you keep working it, it will form an elastic ball of gluten.