Answer:
Ionic = transfer, covalent = share, ionic is between metal and nonmetal, covalent is between two nonmetals. All of these statements are oversimplifications that have no part in chemistry education.
Actually there is very little difference for real bonds. Essentially all bonds involve some degree of electron sharing. "Ionic" and "covalent" refer to ideal bonds much like we talk about ideal gases and real gases. Real bonds have characteristics of both ideal bond types. Real bonds lie along a continuum with the ideal bond types at either end. The general consensus is that only the bonds between the metals in groups 1 and 2 and the most electronegative nonmetals have substantially high ionic character.
The vast majority of bonds are closer to the middle of the range between the two bond types, with a lot more sharing of electrons than transferring. Indeed, some of the sharing of electrons is somewhat one-sided, with the more electronegative element having a slight negative charge, and the more electropositive element having a slight positive charge. Bonds like this are polar covalent bonds.
