The f-block refers to a group of elements in the periodic table that includes the lanthanides and actinides. These elements are characterized by the filling of f-orbitals, which are a type of atomic orbital. The f-block elements are typically found at the bottom of the periodic table and are known for their complex electron configurations and unique chemical properties. The lanthanides, which include elements like lanthanum and neodymium, are known for their use in strong magnets and phosphors. The actinides, such as uranium and plutonium, are primarily known for their radioactive properties and applications in nuclear energy and weapons.