Ion pair definintion in chemistry
As already said, ion pair is a pair of two ions like NaCl. When the pair separates completely into its constituent ions in the solvent (like Na+ &amp; Cl- in water), it is called dissociation.

After dissociation, if the solvent associates itself and surrounds the ions like this-


(Sodium ion surrounded by water molecules), it is called Solvation.
Solvation stabilises the compound and makes it either more reactive or less reactive.