You are most likely referring to the 'accusative case'.
The accusative case refers to nouns...person, place, and thing words...which are the direct object of the sentence. And a noun is a direct object when it is the thing that receives the action of the verb, such as in 'I read a book', or 'She drives a car', or 'I like turtles'.
Book, car, and turtles are the direct objects, and will be in the accusative case.
In Arabic, nouns in the accusative case get one or two fathas (small, straight marks) on top the last letter of the word. If that word has 'al-' in front of it, as in the 'the', then it will have one fatha, making the sound 'a' at the end of the word; if there is no 'al-' there will be two fathas making the sound '-an'.
For example:
Qara'tu al kitaba. = I read the book.
Qara'tu kitaban. = I read a book.