The bonds in BaO (Barium Oxide) are best described as ionic.
Barium is a metal that belongs to the alkaline earth metals group, and it readily loses two electrons to achieve a stable electronic configuration. When barium reacts with oxygen, which is a non-metal, it transfers its electrons to oxygen. This transfer of electrons leads to the formation of positively charged barium ions (Ba2+) and negatively charged oxide ions (O2-).
This electron transfer and the resulting electrostatic attraction between the oppositely charged ions characterize the bond as ionic. Ionic bonds generally occur between metals and non-metals and are characterized by high melting and boiling points.