When used as a noun, the word "rock" refers to a hard geological formation that is millions of years old.
As a form of music, rock is played with one or two guitars, a set of drums, and, perhaps, a bassist.
When a baby is crabby or crying, a mother rocks the baby to sleep in her arms. This is a back-and-forth movement.
She rocked the baby to sleep.
Many back-and-forth movements are described with the word "rock."
You can rock back and forth in a rocking chair.
But if you aren’t careful and you stand up in a boat, a rocking movement can cause you to lose your balance, and you’ll end up in the water.
There are a lot of expressions that use the word "rock."
Don’t rock the boat. (Don’t cause any problems.)
This bread is hard as a rock. (It’s very hard.)
He’s dumber than a box of rocks. (He’s very stupid.)
This building is as steady as a rock. (It has a good foundation; it’s well made; it won’t fall over.)
You rock! (You’re a great person!)
This Thai food rocks. (It’s very good)
We’ve got to rock. See you tomorrow. (rock = leave)
The party was really rocking past midnight. (There were a lot of people there.)
Note: Rock’n’roll music has had a powerful effect on American culture and English language over the last fifty years. You should learn a little about this form of music if you don’t already. In conversation, the word "rock" often comes up as a verb or as an adjective.
