聪明 (cong ming) means smart or clever or wise.
So it can be used to compliment someone like:
"你好聪明！“ （ni hao cong ming)
However, an interesting thing about the words 聪明 is that you will realise there is 耳 (er) inside the word 聪, and 目 (mu) inside the word 明.
耳 means ear and 目 means eyesight. Therefore, there is a meaning behind the word 聪明 that for one to be smart, they would need to have a good sense of hearing and good eyesight. These senses were seen as essential in historical china in times of warfare where having such skills would mean that this person is likely a survivor or fighter.
Nonetheless, in modern times, it has evolved. It now goes beyond having merely just a good sense of hearing or eyesight. It is now imbued with the meaning that one has to be able to pick out the intricacies of a conversation, to be cunning or sly in their conversational skills and to observe the different behavioural aspects of the people they are conversing with. To be able to navigate the political aspect of society is seen as an essential skill to acclaim someone as being clever or smart in China -- thus 聪明!