The relation between the title and the meaning of the movie:
Extremely loud has to be with Oskar's disease and his fear to noise and how these make him upset. It could be also because he and his mother always shout to each other.
Incredibly close is related with the close circle of Oskar's family and how he feel being so close with his mother (at the same house) but so far away because of a bad relationship between them. At the end of the movie Oskar says that as closer he get to his father he is moving away from his mother, and vice versa.