H2O molecule is not linear although it is of the type AB2

The oxygen atom has 6 electron in its valence shell. when it form water molecule (H2O) two of its valence electron is consumed in bonding with hydrogen the remaining four electrons remain as such in form of two pairs called lone pair. Therefore in H2O molecule there are total 4 pairs of electron on central atom(oxygen) , 2 bond pair and 2 lone pair this molecule, this actually correspond to  tetrahedron (with 4 electron pairs) geometry. But the lone pairs will not contribute to the shape of the molecule. Remove 2 bonds from tetrahedron give rise to bent shape of the molecule.