An ionic bond is a chemical bond formed by the electrostatic attraction between two oppositely charged ions. It occurs when one atom donates one or more electrons to another atom, creating two oppositely charged ions. The positive ion is called a cation, and the negative ion is called an anion. The electrostatic force of attraction between the cation and the anion holds the ionic compound together.

For example, when sodium (Na) and chlorine (Cl) atoms react, sodium loses one valence electron to chlorine, resulting in the formation of Na+ and Cl- ions. These ions are then held together by the electrostatic attraction between them, forming the ionic compound sodium chloride (NaCl).