This is the 197th most frequent Turkish word.
gece
Night.
Gece is used here to denote 'the night', the time period after sunset and before sunrise.
Gece yıldızlarla doluydu.
The night was full of stars.
Geceyi here is the accusative form of 'gece', meaning 'the night', referring to a specific period of night.
Geceyi nasıl geçirdin?
How did you spend the night?
Gece is used here to indicate the time period of nighttime for an activity.