The degree of liveliness or bustling atmosphere; the quality of being lively (noun form of 賑やか).
祭りの賑やかさが町中に広がっている。
The liveliness of the festival is spreading throughout the town.
この商店街は昼間の賑やかさが魅力だ。
The charm of this shopping street is its daytime bustle.
彼女はいつもパーティーの賑やかさを楽しんでいる。
She always enjoys the liveliness of parties.