This is the 8895th most frequent Polish word.
sen
"Sen" in Polish means "dream" (as in sleep).
In this sentence, 'sen' refers to the concept of a dream experienced during sleep.
Miałam piękny sen zeszłej nocy.
I had a beautiful dream last night.
Here, 'sen' is used metaphorically referring to a cherished ambition or aspiration.
Moim największym snem jest podróż dookoła świata.
My biggest dream is to travel around the world.
In this context, 'sen' denotes the general state or act of sleeping.