Defect conformal field theories (defect CFTs) have been attracting increased attention recently, mainly because they enable us to bridge the gap between idealistic, highly symmetric models of our world and real-world systems. Real-world systems are generally characterized by finite sizes: impurities, domain walls, defects and boundaries separate regions with different properties and break many of the underlying symmetries.
After a brief introduction to holography and the AdS/CFT correspondence, we will present the AdS/defect CFT duality, a powerful proposal that joins the forces of holography, integrability and the conformal bootstrap program in a framework that is appropriate for the study of defects in real-world systems. Several efforts to apply holographic defects to the study of topological materials and out-of-equilibrium systems will also be discussed.