There is a bit of confusion about what is what. Cornstarch (US) is the squeaky, white, and fine powder extracted from the endosperm of the corn kernels (pure starch). It’s called cornflour (without the space between corn and flour) in the UK. In the US, corn flour (note the space) is extracted from the entire corn kernels and is often yellow. This product is called maize flour in the UK. Read this article explaining the difference between the two products.