This is a technique where the user focuses chakra into their hands and feet using precise chakra control and releases it with pinpoint timing.
The training for this technique is quite arduous, as Tsunade repeatedly came at Sakura with full force to help her learn. Subsequently, the outcome of this training is incredible, giving the user enough strength to easily make gigantic craters or kill opponents with a single strike.
While some may see it as merely superhuman strength, this technique is actually an application of medical ninjutsu that demands excellent concentration and chakra control.
It should be noted that unlike Sakura, Tsunade herself already possesses incredible raw strength, capable of crushing stones in a single hand with nothing but pure muscle power. This strength is later increased to monstrous levels, allowing her to perform feats like lifting and swinging Gamabunta's tantō, creating giant craters and fissures in an area by simply striking it with either her heel or finger, destroying the ribcage of Madara Uchiha's Susanoo and its sword, and sending opponents flying with a flick of her finger with relative ease.