What are ionic compounds?
These are non-molecular compounds composed of discrete positively charged, and negatively charged particles...held together by electrostatic interaction.
The compound is neutral overall, and held together by electrostatic attraction between the cations, the positively charged particles, and the anions, negatively charged particles. Of course within the ionic lattice, LIKE-CHARGED ions electrostatically repel each other, but if you sum up electrostatic attraction versus electrostatic repulsion over the entire ionic lattice, which may certainly be done quantitatively, electrostatic attraction wins, and this is the so-called lattice enthalpy of the salt that binds it together as a solid.
Commonly an ionic compound forms by oxidation of a metal, to give a cation, and reduction of a non-metal to give an anion....and this gives rise to the ionic compound....e.g.
Given their non-molecular nature, ionic solids tend to have high melting points, (and impossibly high boiling points), limited solubility in all but the most polar of solvents (and water is one such solvent), and they tend to be brittle, and crystalline materials.