In the Earth's crust, what is sial?

Sial stands for Silicate (Si) and Aluminum (Al) which are the two most abundant minerals in the Earth's continental crust. The oceanic crust is called Sima (short for silicate and magnesium). Sima is often only 5 to 10km thick while sial can be up to 70km thick. Sial is also less dense than sima. Tectonic plates create the Earth's crust with it either rising or falling into the mantle. The thickest parts of the crust are where there are tall mountains.

https://education.nationalgeographic.org/resource/crust/