A terrane is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or sutured onto the crust lying on another plate. Terranes are significant in geology for understanding the growth and evolution of continental crust, as well as the processes of tectonic accretion.
Reference: Howell, D. G. (1995). “Principles of Terrane Analysis: New Applications for Global Tectonics.” Elsevier.