A connection between two things. Of course, since it's alexboko who's posting this, bond especially means a connection between two atoms. A molecule is several (often thousands) of atoms held together by bonds. A bond can be covalent or ionic, but in practice most bonds have some characteristics of both and are to varying degrees polar. There are also weak hydrostatic bonds and Van Der Waals forces that become important when dealing with large molecules and/or molecules in solution.