Meaning: This means that the waves were crashing against the shore with a lot of force and making a loud, rhythmic sound.
Choice of Words: Waves are large bodies of water that move across the ocean. Crashed means that the waves hit the shore with a lot of force. Loudly means that the waves made a lot of noise. Rhythmic means that the waves had a regular pattern of movement. Ocean drum is a poetic way to describe the sound of the waves crashing against the shore.