means The study of how the Earth's crust is structured and deforms, especially the large-scale movement of the rigid plates that float on the mantle below.

from From the Greek 'tektonikos,' meaning 'of a builder,' rooted in 'tekton'—a carpenter or craftsman, the same word that names a 'tekton' as the builder of houses (and, by tradition, the trade of Jesus). The same root quietly built 'architect' (the 'chief builder'). Geologists borrowed it in the 19th century to describe the Earth as a structure under construction—the crust assembled, buckled, and rebuilt by forces below.