The name for a positively charged ion within a material. The name was given by electrical engineering and physics folks. In some materials holes are mobile, that is that atoms which lack electrons can through thermal agitation steal their neighbor's electron leaving their neighbor as a hole. In other materials holes are relatively immobile.
The ideas of electrons and holes form the basis for the understanding of most microelectronic device building blocks such as the P-N Junction, Mosfet, and the BJT.