The slang term “that rocks” or “something rocks” finds its origin in “rock and roll”.
It means something which is really good and exciting.
When used as a verb “rock” means to play rock and roll music or to rock backwards and forwards, like granny used to do on her rocking chair.
From our younger days and the inception of rock n’ roll the word ‘rock’ has been associated with something which is cool, current, innovative, or up-to-date and therefore very exciting, awesome, pleasing, or fun.
When someone says,“that rocks, Grandma” or “you rock, Grandpa” they are expressing their approval in the strongest terms.
This may refer to something someone is doing and what is happening around you. If something ‘rocks’ it isn’t moving backwards and forwards like a rocking chair – it is happening now and it is exciting and new!
Idioms in Action –
“After riding the Matterhorn at Disneyland, Ben exclaimed, ‘that rocks!'”
“Wow! This chocolate cake really rocks! May I have another slice and the recipe too!?”
As we get older we stop using words like ‘rock’ or ‘cool’ and we notice that new generations form their own words and phrases to express their delight and excitement.
If you’ve ever used the word ‘groovy’ and seen the confused look on your grandchildren’s faces you’ll know exactly what I mean!