Why is the oxygen atom in an alcohol described as having a tetrahedral arrangement?

The oxygen atom in an alcohol is described as having a tetrahedral arrangement because it possesses four electron pairs—two bonding pairs and two nonbonding (lone) pairs—that adopt an $s{p}^3$ hybridized geometry to maximize their mutual separation.12

According to VSEPR theory, these four electron pairs naturally orient themselves toward the corners of a tetrahedron around the central oxygen atom. While the electron pairs themselves adopt this tetrahedral disposition, the actual molecular shape is determined by the positions of the atoms; in alcohols, the presence of these lone pairs and the bulkier alkyl groups (compared to the hydrogen atoms in water) influence the specific bond angles, such as the 108.9° angle observed in methanol.21