This is the 2757th most frequent Polish word.
fal
"Waves" (plural form of "fala").
In this context, 'fal' refers to the wavy texture of hair, using the genitive plural to describe the arrangement.
Włosy układały się w piękne fale.
The hair formed into beautiful waves.
In this sentence, 'fal' is the genitive plural form of 'fale' (waves), used to indicate possession or origin of the sound.
Na plaży słychać szum morskich fal.
On the beach, one can hear the sound of sea waves.
Here, 'fal' indicates the genitive plural of 'fale' (waves), referring to radio waves in the context of technology.