When playing piano, there are two ways in which your hand can move across the keys: they can shift or they can cross. When your hand shifts, it is sliding across the keys to a new position. Crossing occurs when you move one finger over or under another finger, like when you move your third finger over your thumb in a descending scale. In this video, Josh Wright of joshwrightpiano.com explains both shifting and crossing, and the best way to use each when playing piano.
Playing Piano: Shifting vs. Crossing
I think I naturally do the shift at times and mistakenly cross at other times. That may be why I often feel unsatisfied with my arpeggio or run passages. I had not consciously thought about it this way. Apparently, that subtle difference for the hands makes a big difference in smoothing it out. Thanks for the tip!