This word is a very good example of the importance of collocation in English ie which words go together with what other words. Yes, it means organised/co-ordinated, but it is by no means a synonym of these words. The adjective 'concerted' is almost always used with the word 'effort', plus a few other words such as action.

it means together, co-ordinated, and in the same direction. "Let's all make a concerted effort to make sure the project goes smoothly". "The charities were involved in concerted activities to help the flood victims". Think of a 'concert' where all the players are playing the same tune at the same time.

"Organised." You hear this in the phrase "make a concerted effort". So everyone works "in concert".