What does atomic radius and ionic radius really mean to you?
Atomic radius is an estimate of an atom's size, as the electron cloud has no sharp boundary and an individual atom's size cannot be precisely measured. It is determined by measuring the distance between atoms in a combined state. For non-metals, it refers to the covalent radius (half the distance between two atoms in a single bond), while for metals, it is the metallic radius (half the internuclear distance in a metallic crystal).
Ionic radius refers to the size of an ion, estimated by measuring distances between cations and anions in ionic crystals. A cation is smaller than its parent atom because it has fewer electrons while its nuclear charge remains the same. An anion is larger than its parent atom due to increased electron repulsion and a decrease in effective nuclear charge.
Explanation
The answer defines both atomic and ionic radii based on the textbook context. Atomic radius is defined via covalent or metallic radii due to the lack of a sharp boundary for the electron cloud. Ionic radius is defined by distances in ionic crystals, explaining the size differences of cations and anions relative to their parent atoms.