What did Zacharias mean when he called the baby in Mary's womb a horn of salvation? In order to answer that question, we must turn to the Old Testament to see how that figurative expression was utilized.
In the Old Testament, horns in many instances carried connotations of strength and honor (Job 16:15; Psalm 75:5-6; 148:14; Lamentations 2:3). God is described as being the horn of salvation in Psalm 18:2. Hence, the psalmist calls Him the mighty savior.
The title given to God in Psalm 18:2 is applied to Jesus Christ by Zacharias. In an indirect fashion, he is calling Christ God. He is the mighty savior of the Jewish people. He is victorious over darkness and sin. He is deserving of honor.
The horn of salvation is associated with the lineage of King David. It also might point to in an inexplicit manner a hymnal of praise to God sung by the mother of the Prophet Samuel ("...will exalt the horn of His anointed," 1 Samuel 2:10).