A moment is an ambiguous unit of time, it could be anywhere between a few milliseconds and 3 seconds.

A second is a precise unit of time, precisely equal to 9,192,631,770 cycles of the radiation that gets an atom of the element called cesium to vibrate between two energy states¹.

A moment is an ambiguous unit of time, it could be anywhere between a few milliseconds and 3 seconds (not necessarily limited to 3 seconds).

A second is a precise unit of time, precisely equal to 9,192,631,770 cycles of the radiation that gets an atom of the element called cesium to vibrate between two energy states¹.