It's very easy to confuse these terms when you begin using iClone. At first glance they seem to be one and the same, but in actuality they are two different concepts that concern characters.
Motions are prerecorded animations that are packaged into drag and drop files that can be used with a character. For example, a talk motion would have the character act out part of a conversation as though they are talking. Hands and body movement along with head movement will all be parts of the motion.
Motions have certain features that can be modified:
Speed Faster or slower
Reverse (when available) runs the motion backwards
Timing The motion's place on the timeline
Lead In Or Mixing for multiple motions
Motions start as animations. Motions are created through key frame manually, by motion capture (mocap), or by other animation programs, or by a combination of these methods. Being prepackaged has its advantages, but also has its drawbacks.
Note
While the packaged motions are much easier to use they are limited to what animations they contain until you learn to cut and edit motions on the timeline, and even then there is only so much you can do to alter a motion.
Animations are what we create with the timeline and key frames which can be saved as motions. Props with built-in actions such as a door that opens are animations created in other programs.