A transition in which an element’s geometry transforms continuously into a new form, so the before and after read as the same object.
The play button morphs into a pause button, so the control reads as one object with two states.
Morphing earns its complexity when object permanence matters: the user should believe the card became the detail view. If the two states share no real structure, a morph invents continuity that doesn’t exist; use a crossfade and let the change be a change.