This is the 763rd most frequent Lithuanian word.
feisbuke
"Feisbuke" means "on Facebook" in English.
In this sentence, 'feisbuke' is in the locative case to indicate the location where the action (writing a message) is taking place, i.e., on Facebook.
Aš rašau žinutę draugui feisbuke.
I am writing a message to a friend on Facebook.
Here, 'feisbuke' again uses the locative case signifying the platform where the interesting pictures are visible.
Matau daugybę įdomių nuotraukų feisbuke.
I see many interesting pictures on Facebook.
This sentence uses 'feisbuke' in the locative case to emphasize the source (Facebook) where the news can be found.