This is the 7527th most frequent Russian word.
дима
"Дима" is a diminutive form of the male given name "Dmitry" in Russian.
In this sentence, 'Дима' is used as a proper name.
Дима идёт в школу.
Dima is going to school.
Here, 'Димы' is the genitive form of the name 'Дима', indicating possession.
Это книга Димы.
This is Dima's book.
In this example, 'Диму' is the accusative form of 'Дима', used as the direct object of the verb.