That's the bee's knees!

What does the saying "bees knees" mean?

'That's the bee's knees' which means it is excellent, the highest quality.

The phrase 'the bee's knees' came from the 18th century and it was a fanciful phrase that referred to something that didn't exist. A boss would send an apprentice to the store to pick up a left-handed hammer and a bag of bee's knees.