Shannarō (しゃーんなろー) is Sakura Haruno's catchphrase, something she would shout either when she is too angry or excited. She often uses the phrase when she punches Naruto Uzumaki out of anger. Sakura punches Naruto and uses the phrase when he insults either her or her master, the Fifth Hokage, Tsunade. She also does it sometimes when he demonstrates his perverted techniques or does something else shameful.
In Part I, the phrase was often used by Inner Sakura (内なるサクラ, Uchi Naru Sakura).
Shannarō has no literal meaning, but can translate into Hell yeah!, Hell no!, or Damn it! (depending on the situation).
In the English dub, the phrase was replaced by a forceful Cha, which Sakura has a unique way of saying.
Shannarō and Cha are spoken by Sakura usually to add a comical relief in the series, though she is seen speaking it even in tensed situations, such as in her fight with Sasori. It also accompanies Sakura's punches when used on an obstacle, like the giant boulder blocking the Akatsuki hideout in the Land of Rivers.
In the epilogue, Sakura's daughter, Sarada had likely inherited this catchphrase from her, as shown when she said Shannarō! after she stated that her and Boruto's relationship with their respective fathers is similar.