Girls' Festival; Dolls' Festival
Refers specifically to the March 3rd seasonal festival (節句) for girls, also known as ひな祭り. The term 三月の節句 is a traditional name for this celebration.
See also: ひな祭り (ひなまつり)
Many households display hina dolls for the Girls' Festival.
ひな祭り is the more common modern name for the same festival. 三月の節句 is a more traditional, formal term.
三月 (March) + の (possessive particle) + 節句 (seasonal festival). One of the five traditional seasonal festivals (五節句).