This is the 4449th most frequent Turkish word.
annesini
"Annesini" means "his/her mother" in Turkish, used as the object of a sentence.
In this example, "annesini" refers to the object of "ziyaret" (visit), which requires the accusative case to show the object of visiting and indicates possession.
Kız arkadaşım, annesini ziyarete gitti.
My girlfriend went to visit her mother.
In this sentence, "annesini" is in the accusative case, denoting that the mother ('anne') is the direct object of the verb "seviyor" (loves).
O çocuk, annesini çok seviyor.
That child loves his/her mother very much.
Here, "annesini" again denotes the direct object of the verb "çağıracağım" (will call), showing possession (his/her mother) and the accusative case.