Nonconcatenative morphology

Nonconcatenative morphology, also called discontinuous morphology and introflection, is a form of word formation in which the root is modified and which does not involve stringing morphemes together sequentially.

It may involve apophony (ablaut), transfixation (vowel templates inserted into consonantal roots), reduplication, tone/stress changes, or truncation. 

It is very developed in Semitic, Berber, and Chadic branches of Afro-Asiatic. It also occurs extensively among other language families: Nilo-Saharan, Northeast Caucasian, Na-Dene, Salishan and the isolate Seri (in Mexico).