This is the 1590th most frequent Polish word.
internetu
"Internetu" is the genitive case of "internet," meaning "of the internet" in English.
Here, 'internetu' is used in the genitive case, indicating possession or the lack thereof, commonly used after 'mam' for an entity not present.
Nie mam internetu w domu.
I don't have internet at home.
In this sentence, 'internetu' is in the genitive case as part of the verb expression 'używać', which requires the genitive to specify the object being used.
Używam internetu codziennie.
I use the internet every day.
Here, 'internecie' is in the locative case, which is used to indicate location or context, as governed by the preposition 'w'.