The d-orbital is a type of atomic orbital that can hold a maximum of ten electrons. It is part of the electron configuration in atoms and plays a crucial role in the chemical properties of transition metals. D-orbitals have a more complex shape than s-orbitals and p-orbitals, which allows them to participate in bonding and influence the behavior of elements. There are five different types of d-orbitals, labeled as dxy, dyz, dzx, dx²-y², and dz². These orbitals are important for understanding the periodic table and the formation of various compounds. The presence of electrons in d-orbitals contributes to the unique characteristics of transition metals, such as their ability to form colorful compounds and exhibit variable oxidation states.