Cornflour is made from finely ground corn; thats what it looks like to me.. It's used in cooking as a thickening agent, and also in HP Sauce.

What I used to do with it though is to make a saturated solution of it with cold water. This has the interesting properties of flowing like a liquid, but fracturing like a solid when pushed around too fast and is an example of an iostropic liquid (in contrast to a thixotropic liquid like tomato ketchup.

North American cooks should note that cornflour is known on this side of the ocean as cornstarch, and should not be confused with cornmeal, which is more coarsely ground and does not have the thickening powers of cornflour.